Hi JDad,
Much good advice here, but since I play Cam the Critic role at Axiom, I feel I should point out the big disadvantage of using the phantom mode without a center channel speaker.
It works fine if you (and only you) are sitting directly between the main left and right front speakers, which form the "phantom" image of a singer or actor's voice centered between the two stereo speakers. However, for anyone sitting to either side, the phantom image collapses to the closest left or right speaker, just like it always did in pure stereo days.
The huge advantage of a center channel is that it locks the singer's voice or dialog voices at the screen or in the center of the stereo soundstage, even if you are sitting way to one side of the room.
