Mmmm I thought most people in Smart land did it the otherway around, with the amp strapped to the back of the seats and the subs under the seats ???
Personally I have most of the stuff under the dash or in the foot well as access to under the seats is restricted by the fire extinguisher. Although I think I did put the Nokia and Sony Aux in boxes under there.
Do you really need more sound with the sound upgrade you have ??? I've never seen the need myself, having said that I hardly use the empeg in the car these days, mostly I listen to the Radio on the way to work though the Sony HeadUnit.
This Guy's leads may come in handy, I have one so I don't blow the tweeters, works very well.
I didn't use the facia adaptors you can get, they only did them in black or blue when I fitted mine (my dash is Grey), and as I had to butcher the ashtray drawer to do a dual DIN job I just got the dremmel to a radio blank panel from my local dealer. Looks OKish.
Cris.