Using the Zen POWER9 in BMWs

by Ken Ward, Educar Labs

Back in the early 2000's, BMW worked on completely reworking their infotainment and audio architectures. They started putting 4" mids in the doors, and 8" woofers underneath the front seats. They launched the iDrive infotainment system. They dropped analog preamp signals and switched to MOST 25 networking (the most recent BMWs no longer use MOST, and have switched to another network technology).

It took a few years for the aftermarket to catch up to all these changes. I bought a 2007 E91 3-Series Touring new off the lot, discovered that nothing fit at the time, and started testing products to see what worked (I actually tested one of the early Mobridge DA2 network preamps in that E91 - the product which became the DA-G2 Standard).

The speaker provisions in these cars can deliver great sound without custom modifications (I know, I've done hundreds of them!) Many of the best-sounding upgrades to these BMWs used the Mobridge DA1 "digital preamp". In recent years, the DA-G2 Standard and Pro models have been used with great success. In 2026, Zen Audio introduces the Zen POWER9 MOST 25 network amplifier. I've been testing the ZP9 in my current BMW, an F34 335GT. 

The current BMW test rig

 

Initially in the F34, I removed the 688 MOST 25 amp and used a Mobridge DA1. Later I tested (and approved) the Zen 25 preamp with DSP in its early days. Then we reinstalled the OEM 688 amp and used it as an upmixing processor, going high-level into the Audison gear (and a Toslink input from the Audison B-CON for reference)

Currently, we've eliminated that OEM amp and plugged the Zen POWER9 directly in its place. We started off without the 10" trunk sub in the picture - I ran the mono channel of the ZP9 into the center speaker. When set to "Center", it's 125W RMS and uses the Zen Upmixer center processing. Then I tested the mono channel delivering 500 watts to my sub. Finally, I put the mono channel back on my center speaker, and used my dedicated sub amp on the sub. 

The tweeters in the front doors and in the center location were run in an active configuration, with new wires run into the doors and dash. I would not run those wires into the doors again - it's a great deal of work, and I'm not convinced of the benefit. With 4" mids, we just don't have to play these tweeters incredibly low. For these tests with the ZP9, the Audison passive crossovers were installed from their BMW kits. This let us get back to the nine original channels of the stock system (plus the subwoofer).

The plug-and-play harness made the installation a breeze. All that was needed was power to the battery (I run the ground to the battery location as well), and fabrication of a mounting plate. 

The Zen POWER9 in my BMW 335GT

I confess to being a bit skeptical about Nav-TV getting into the amplifier business - but I know from an engineering perspective, a lot of building Class D amps is selecting a great chipset, and this amp uses the same chipset as some highly-regarded European SQ brands. Turns out, they used two technologies that I've always favored in car amplifiers - stiffly-regulated power supplies, and Class H "look-ahead" operation. The ZP9 really does sound great - if you're interested in what these technologies do, there's more explanation available here. 

Here is some information on the BMW "harman/kardon" sound package, and three upgrades I've tested and I recommend:

 

OEM "harman/kardon", BMW S688

In my car, all seven cabin speaker midranges are paired with a tweeter. In older E-series BMWs, the center midrange and the rear surround midranges did not have tweeters installed next to them (adding a tweeter was a common center-channel upgrade). When upgrading, coaxials are good to use in the rears to save on complexity.

This system's amp sends 25 watts to each of the 7 mid-tweeter channels, and around 100 watts each to the two underseat woofers. The resulting 375 watts is pretty good for an OEM system, even if it's far below what BMW marketing claims.

However, when you play a 4" midrange down to 80 or 100 Hz - as many h/k systems in BMWs do - distortion results at higher listening levels. Raising the crossover "handoff" point from the door midranges to the underseat woofers addresses this issue. 

You may ask why BMW has two sets of rear speakers in these systems - great question! One pair has a more traditional sound, and one pair is used for ambience signals.

NOTE: In convertibles, the rear deck speaker pair is deleted. 

 

 

System 1: Zen POWER9 in place of the stock amp, New Speakers

The Zen POWER9 ups that 375 watts to 1380 watts RMS! The resulting sonic improvement is incredible. See the diagram below for the power ratings of the various channels. With this kind of power, many BMW owners upgrade their speakers as well. The stock speakers are not terrible, but tend to deteriorate after only a few years (the worst offenders are the center channel and rear deck speakers, which receive lots of UV exposure). Several quality speaker manufacturers now offer BMW upgrades. When using the center speaker, use as good-sounding a center speaker as you can. Great door speakers paired with a merely-decent center speaker will only get you decent sound.

 

NOTE: With X3/4/5/6, the D-pillar surround speakers are not exposed to UV and can be used without concern as ambiance surround speakers. 

 

System 2: Zen POWER9, New Speakers, Trunk Sub, Center Delete

This is very similar to System 1, but In this system we don't retain a center speaker (we tune for the driver). We use the mono channel of the ZP9 in Subwoofer mode, powering the new trunk sub with 500W RMS. 

In this scenario, the trunk sub level is controlled by the bass control in the iDrive tone menu. 

 

The underseat woofers now work as midbasses with a bandpass (I like 50 to 200 Hz in most BMWs). This gives us the best of both worlds - great midbass and deep sub-bass. 

 

System 3: Zen POWER9, New Speakers, Trunk Sub on External Amp, Center Retain

In this system, we do retain a center speaker, and we add a trunk sub on its own dedicated subwoofer amp (not included). We use the Channel 10 RCA out to supply DSP-tuned signal to the sub. The mono channel of the ZP9 is in Center mode, powering the center speaker with 125W RMS. 

With System 3, we can set the first tuning preset for a driver tune with the center muted, and the second tuning preset with the center playing an upmixed 2-seat presentation. This lets us switch between the two with the "Surrround On/Off" setting in the iDrive. 

 

 

In this system, the output level to the external sub amp is controlled by the bass tone control in the iDrive tone menu. 

 

Built-in Zen MOST 25 Network Preamp

The Zen POWER9 has a MOST 25 network preamp built in - the input is always flat, aligned, two-channel sound. There's no input correction needed at all. Just set it to "BMW" in the software! If you're wondering what a Network Preamp does, there's more information available here. 

However, because the MOST 25 network carries chimes, parking sensor tones, handsfree calls, and nav prompts on individual audio channels (seperate from the two-channel music audio), the installer can use the adjustments in the Zen DSP to route these to any desired output channel - and to adjust their level individually. This is a huge benefit compared to the high-level integration I'm used to. 

 

Zen DSP Tuning

The Zen DSP app has all the tools needed to make a BMW sound great. The standard DSP toolbox of level, crossover filters, polarity inversion, and delay are all here. 

First- and second-order all-pass filters are also available, as are shelf filters. (All-pass filters give you targeted phase inversion of specific frequencies, at variable rates of change).

Unlike most DSP products, the Zen DSP includes a global EQ with the same number of EQ "points" as the channel EQs have.

The two channels of audio from the network preamp can be routed as you wish. Nav-TV has used an innovative combination of IIR and FIR filters in the Zen DSP, which really get a lot of functionality out of this DSP engine. Of course, the ZP9's built-in network preamp means that no DSP resources have to be held in reserve for input-signal correction. This is a design requirement in universal DSP amps - but the more resources assigned to input correction, the fewer resources are available for acoustic tuning. 

 

Zen Upmixer

The purpose of the Zen Upmixer is to let the system tuner set up the system for good stereo performance, regardless of the listening position. (This is often called a "two-seat tune".)

Stereo has two channels, and information common to both is considered "centered".

 

To accomplish this, the Zen Upmixer gives us an assignable center output and assignable surround channels. The center channel focuses on content the recording engineer intended to be in the center of the stage - the "common" content. This lets us tune the system symmetrically, so we get the same sound from either seat. (This is where the all-pass filters really come in handy - experienced tuners can use them instead of delay to address phase issues.)

When the mono channel of the ZP9 is set to "center", the output is limited to 125 watts.

With the ZP9, channels set for "surround" have "full differential" or "partial differential" modes. That means they remove , or reduce, the common content. Full differential cancels out any center-stage information, so these speakers will never compete with the center speaker and pull the stage aft. Partial differential attenuates center-stage information by about 50%, rather than cancelling it completely. Since most recordings have a lot of common content, "full differential" is significantly quieter, and sounds very different than many users expect. Partial differential sounds much more recognizable (and is louder!) but some feel it isn't as good at widening the stage.

In either mode, the ambiance channels are automatically delayed significantly relative to the front speakers - to "decorrelate" their sound from the front stage sound. In BMWs with two sets of rear speakers, you can use the rear-side speakers for ambience and slightly better stage width, or you can use the rear-deck speakers for surround and use the side speakers for normal stereo (this gets you slightly better sound for the rear-seat occupants).

In situations where you only have one set of rear speakers, "partial-differential" is a good compromise ("stereo" is, of course, louder).

 

Conclusion

Upgrading BMW sound back in the early 2000's was a mysterious and difficult affair. Now, several speaker manufacturers offer BMW bolt-in, plug-in speakers - but signal and amplification are still the limiting factors.

If you have a BMW with MOST, this is a path you should really consider. (To check if your BMW is covered, click here.)

 I've been really happy with my Zen POWER9 - it's on instantly (I think it turns on as soon as I unlock the door!) and all my non-entertainment sounds work and sound as they should. It's noise and distortion-free. I've got the two-seat tune set up for Preset 2, which I access by turning on the "Surround" function in my iDrive tone menu. The Zen POWER9 MOST 25 is a first-rate solution for upgrading MOST BMWs - it saves a lot of work, with no sonic compromises and several advantages. 

To order the Zen POWER9 MOST 25, or for more information, click here.