I've got to say, as much as I enjoy ProTech's avatar, I'll respectfully disagree also.
You did not say what your music/HT ratio is. But John is on-point (as usual) about the sub. You cannot get a full home theatre experience without a sub. You can set your receiver for a "phantom" center channel to fill in and center the dialog, but you can't get the frequency response without a sub.
And I think music listening will benefit more from a sub also. Most music is recorded in stereo, so the engineer was thinking of full-range two-channel. You could make a case that adding a center will actually muddy-up the music imaging, and it certainly will not extend the bass response.
But, as others observed, a lot depends on your room, listening habits, placement, and personal preference. You asked for opinions; mine is free, and worth the price charged.
You might also pose the question to other, more expert resources, like the Axiom staff.
