Hi,
It sounds like you just need to find yourself an AV amp / receiver with multi-channel pre out sockets. Plug the front Left and Right pair into your stereo amp and your away. It might be worth looking for an amp that has a mic and automatic EQ as this will help to balance out any differences in response between the two amps and the two different types of speaker. It'll help to integrate them better and also help to counteract problems with your room's acoustics. Audyssey (Denon, Onkyo), MCACC (Pioneer) and YPAO (Yamaha) all seem to work pretty well.