Sounds like an awesome project!
While I don't currently own a DVD-A/SACD player or listen to 5-channel music regularly, I can say from limited experience that I would definitely put together a multi-channel system using identical speakers. My M60s and VP-150 center are quite well timbre-matched, but I can pick out the inconsistencies across the front soundstage if I try to listen to multi-channel music critically. You just can't expect speakers of two different sizes, shapes and port configurations to sound exactly the same. I always revert back to 2-channel for music.
Since you are setting this system up for music only, you don't have to buy a special center channel to fit on top of the TV, or otherwise compromise the ideal placement of the center. Therefore, I'd definitely recommend picking up five matching speakers placed just where they should be, and a nice sub.
Just my $.02. Good luck!
