Just to echo the comment that if you are going to go down this route then look for an amp with 'AV bypass mode', it makes things much less of a faff.
Originally I ran a Yamaha ESP 800, it handled the decoding and only has 3 channels of amplification. I used it to drive the centre, rears and sub. It was hooked up to a Roksan Kandy mk III for the fronts an for listening to stereo music.
In the end I found the hassle of switching everything on, getting sound levels balanced etc just to much of a chore. So I sold the the ESP 800 and bought a Yamaha DSP 765.
This time I ran both amps seperatly. I had the rund of speaker terminated with banana plugs. And depending on which amp I was listening to I just swapped the cables on the front speakers. Again after a few months of this I got sick of it.
Ended up selling both amps and getting the most musical amp I could afford at the time. Picked up an Arcam AVR270. Very nice amp but music is not in same league as the it was when going through the Roksan
In the end I comprimised on sound quality. When I eventually move to a bigger house I will do a bit of shopping and have 2 systems