This is a tricky one simply because I don't think the product you could use is made anymore! Yamaha used to do a 3 channel amp to power the center and surround speakers. It plugged into one's stereo amp via the tape loops. You set your stereo amp at "12 o'clock" and then just use the yamaha as you would a fully fledged surround amp.
This was the only choice back in the day for those of us that wanted a decent stereo set up but hankered after some cinematic excitement at the same time.
I bet you can find one if you shop around on ebay.
I think it might also be poss to get a surround processor (as the pre amp I think) plus a bunch of naim power amps for each channel. This of course would sound great but take up a load of room and cost quite a bit too.
Hope all this helps. Anyone else out there got any ideas?