Oh my god, do I feel stupid now... perhaps I should've looked in my own fscking trunk before posting that cry for help.

After all, perhaps I could be a victim of the standard installer-thought-he-was-too-smart-for-the-manual-and-therefore-ignored-the-directions-to-attach-supplied-grounding-rca-cords-to-amp...

Hmm, what are these extra cords lying around back here?

So, I spent all of 60 seconds detaching the leads from the empeg to the amp and inserting the grounding leads inline and attaching the grounds to the amp, and... voila! Distortion is gone, front and rear channels sound great! I guess I'll have to send a nasty letter to the installer's boss. Especially since I pointed out the goundling leads to him and explained their significance. Of course, the quality of the rest of the installation was so high I can hardly complain.

Thanks, empeg, for the great product, and thanks, community, for this wonderful resource. Now I just have to figure out how to keep that single 10 inch sub from shaking my poor Altima to pieces :)