Customer complaints about the EPS system DIRAC processing... no-impact bass, somewhat dull vocals, uselessness of the EQ adjustments to get it right.
The cause of all those issues is located in the EPS OEM amp. Unfortunately the OEM amp cannot be removed/replaced as it is part of the MOST-ring and controlled by proprietary digital inputs.
Either a $700 MOST converter must be used or simply the iDrive CIC could be coded to output balanced, low level analog signals as the standard HiFi OEM sound system so the OEM amp can be unplugged and replaced.
Because the customer brought a full set of JL Audio HD amps (two HD600/4 and one HD750/1) plus a Stealthbox, this was a no-brainer: coding to HiFi.
Custom JL Audio PnP Quadralock-to-RCA harness:
Remove CIC and plug RCA PnP harness:
Run RCA extension cables to trunk, including tapping pin 13 (thin black wire) of the Quadralock for the OEM remote:
Unplug OEM amp, terminate MOST connector with termination loop, create HD amp platform and OEM audio harness (change 9-channels to 7 channels outputs) and stack the HD600/4:
Replace standard left OEM trunk trim with OEM CD Changer trunk trim to make space for the stacked HD's and install HD750/1 to power Stealthbox:
1) All OEM speakers were kept, even the underseat woofers.
2) iDrive CIC was coded from M Individual Sound to HiFi thus no more OEM 7-band EQ, just Bass and Treble adjustments
3) Center OEM speaker was handled by combining the front left and right CIC outputs into one HD600/4 channel. This sounded quite good with music but was troublesome for Bluetooth phone conversations. So the center speaker was unplugged until a proper processor is installed.
How this exercise sounded? Quite good considering that this a non-processed, flat system.
Voices are clearer, underseat OEM woofers midbass is tighter and louder. Definitely an improvement in apparent clarity and bass impact which again demonstrated that the limiting factor of this system is the OEM amp and not the Individual Audio OEM mid speakers. Treble needed to be adjusted to less highs, a byproduct of removing the DIRAC processing. The Stealthbox more than satisfied any need of sub bass, which really put this upgrade over the top relative to its simplicity.
There are sufficient adjustments to get a loud and clear (in that order) system in here, however this is a much better platform now than the OEM to add any of the high-grade DSP processors available in the market.