Fooljam is partly right. The JL amp is the weakest part of the systems.
1) It's 9 million times better than stock amps
2) The differences between amps are compressed into a much tighter window than the differences between speakers.
We have no problem acknowledging that the XD amps are not as high-performance as, say, the Arc Mini series (which is not Class D). But there aren't many 6-channel options, and the XD doesn't suck. It just doesnt' sound as good as a $800 or $1000 6-channel amp that's bigger.
Musicar Northwest Portland OR musicarnw.com
High-performance audio for BMWs