Wierd signal levels from CD Player

I just installed an amplifier in my '06 Package 4 (no NAV, no JBL) and I'm
noticing a strange phenomena with the signal levels coming from the CD
source. Some CD's seem to put out the same level of output as the other sources (i.e. FM/AM) but other CD's (store bought not self-burned) seem to have much
lower output levels. I did not notice this when listening to the same CD's on other stereo systems, so I think it's got something to do with the CD output section of the factory head unit.

Another strange phenomena....the apparent bass output seems to drop off when you exceed certain volume levels (e.g. 40 or more)...this seems to be tied somehow to the "ASP" function of the factory head unit, because, when I turned ASP off, it seemed to lessen (but not eliminate) the effect.

Does this sound familiar to any of you out there?
If so, is there a remedy?