I wrote a post on audio upgrades for the NC in a different topic recently, might be relevant:
Personally I have disabled the speakers between the head rests as they completely ruin the stereo image. Stereo image is dependent on a left and right speaker. Pretty much all music is at least stereo. And as a RHD-driver, when sound plays on the right speaker you’ll hear it on the right rear side, the problem is with sound playing on the left side; you’ll still hear it coming from the right, although from the rear.