A 20' high ceiling isn't a typical "home theatre". IF it's just a "great room" scenario that is being transformed into a "home theatre" then as the others have mentioned, a lot more information is required. The 20' ceiling height is what is raising all the red flags. A 20' ceiling without a properly engineered approach won't end up being a great home theatre experience. If the room is 20' high ans also really large, the need for an intelligent deisgn is all that more vital. Large rooms require careful attention to managing the reverberant field as well as dealing with low frequency issues such as standing waves, lobing, and comb filtering. Always address or attempt to "fix" the room first ,, saves a lot of money trying to band aid acoustical problems with electronic solutions that often only mitigate the problems