Big room. Ceiling height?
I would consider something like an HSU VTF-15h subwoofer for about a grand, another 800-1k for a receiver : Yamaha , Denon, pioneer, onkyo, and Marantz are all contenders.
1500.00 or so for your front 3 speakers and 500.00 for the rears.
I'll not make a specific recommendation for speaker brand as they are a very subjective item. Listen to as many as possible and decide for yourself. Internet direct has some great sounding stuff and many of the manufacturers have flexible if not free home trials.
Have fun and take your time deciding.
Cheers, Mac