Phasecorrect,
I couldn't tell if $10K - $15K was the budget for the whole system or just the video portion.
FWIW, I have a similar sized room and found a significant improvement in surround envelopment when I went from a 5.1 to a 7.1 system. I don't know if that was a pecularity of my particular room, a characteristic of rooms of this general size, or whatever, but I was not a happy camper with the 5.1 setup.
I recommend getting a 7.1 set-up, or at least pre-wiring for that for easy expansion as budget allows.
Also recommend getting a PrePro/Receiver than can do justice to generating 7.1 outputs from the sources you would envision using. For example, I do not consider duplicating the side speaker signals into the rear speakers to be a very good way of achieving 7.1 sound.
Bruce