I did that about fifteen years ago. The main thing is: ditch the center channel. If you have really good speakers and placement, keep them and bridge the R/L speakers in lieu of a center channel. You stereo will stay perfect that way, and you'll hardly miss a center channel (certainly better than a mismatched one). Add the rear speakers and essentially run a quad system.
This lesson did not come easily. I started with five full range Thiel speakers .... the sound quality was superb .... the stereo imaging sucked until I removed the center speaker and experimented with bridging, which I could do either in the Oppo or in the surround preamp. The main problem is that surround is mixed to a set speaker placement that has the L/R speakers much further apart and forward of the center to get decent surround imaging. It sucks for stereo. If you keep a center but put the L/R in their normal stereo position, you get a cramped front soundstage and slightly uneven side imaging ... more front/back than it should be.
I've never seen this recommended anywhere but believe me it is real. I found the same thing in three separate rooms as well as with alternative speakers. Try it for yourself. You'll find I'm right.
This lesson did not come easily. I started with five full range Thiel speakers .... the sound quality was superb .... the stereo imaging sucked until I removed the center speaker and experimented with bridging, which I could do either in the Oppo or in the surround preamp. The main problem is that surround is mixed to a set speaker placement that has the L/R speakers much further apart and forward of the center to get decent surround imaging. It sucks for stereo. If you keep a center but put the L/R in their normal stereo position, you get a cramped front soundstage and slightly uneven side imaging ... more front/back than it should be.
I've never seen this recommended anywhere but believe me it is real. I found the same thing in three separate rooms as well as with alternative speakers. Try it for yourself. You'll find I'm right.