Thanks again Mike

I did the setup as you suggested and, while it took some tweaking with the amp settings, I have a sound I'm very happy with. The behind the seat speakers have really perked up and add a great fullness they never did before.

At this point I don't think I'll miss the subs but I can always put in a second amp just for them. If I understand correctly I can just run RCAs from the new Alpine amp to a mono amp and run the subs from there. Sound reasonable? I think I can also pick up the sub output from the head unit but that would mean running more cables through the console.

I'm still monkeying with the fader and balance controls which don't seem to be working as usual.

Now it's time to settle everything in the trunk. Lot's of wires to organize! I mounted the amp on a piece of gray carpet-covered plywood and am planning on using the idea from here of industrial strength Velcro to hold it in place on the carpet. I'm not sure about the crossovers...options include: also mounted on a piece of wood and Velcro'd beside the amp?...Mounted to a board mounted to the bracket from the stock amp? Any other suggestions anyone?

Thanks again to all who helped, especially to Mike for the early help and the suggested layout, Monolith for the early direction and info, and WB-MZ for the idea that helped me understand better what I was doing or trying to do.

This board has been an amazing source of information and help over the 13 years I've had the M. I'm usually willing to try anything with the car knowing I can either find info in the archives or someone willing to give a hand.