Lost sound to drivers side door/missing amp

[Aldog87]

After getting the hood and roof painted on my 2012 135i (46K miles), the sound output to the driver's side door is way off. By that, I mean it's mostly just the tweeter with very little output to the mid-range speaker. I think it's just a coincidence that the sound went haywire while at the paint shop, but whatever. After a stop at the dealer to see if they could find anything obvious with the system, we agreed that the problem was probably with the amp. Since the car was originally spec'd with the HK upgrade, i went ahead and purchased a used, replacement amp. Well, much to my surprise, when I pulled the trim off in the right side of the trunk, there was no amp there. Not even any wiring harness in place to install the replacement amp. So, I've got two questions.

1) Did Harman Kardon spec'd cars come without the factory amp?

2) Is it possible that the sound trouble is from the original, in place, factory stereo head unit?

Oh yeah, just as an aside, the sound is marginally better when playing CD's or from the on-board MP3.

I'll probably end up taking the car to a local audio shop, but hopefully I can get some input on what might be wrong.