Originally Posted by Exwoodchuck
In BMW's opinion, this is an 'electronic', and thus isn't returnable.
I'm confident that we can come up with a workable solution. I'm also confident that BMW won't come up with a fix, because they believe there is not a problem.
The problem for you and BMW is that this retrofit is neither Stereo NOR HiFi, it's a little of both. ISTA/P can toggle the output between either but not adjust individual variables such as those you discovered (well it could be programmed to do so).
I speculate that immediately post 03/09 BMW decided recoding was a better idea, as this is the best solution for SQ. Then later discovered it was detrimental to PDC output, and thus withdrew the instructions to code the vehicle, returning to the pre 03/09 solution.
It is possible that the 8 jumpers in some magical combination can flatten the EQ curve but without someone like montr and his test equipment, we won't know what the effect of each is.
I think the best solution right here and right now is to leave it coded to HiFi, and adjust the PDC level back to e90_stereo. Try that and that alone, and report back?