I agree with Mark (because he can always use the support).
I'm in about the same situation he described. I would be VERY surprised if there was a significant or distracting difference in timbre between the ti towers and the V3 center. Remember that speaker placement is always going to make a difference; when you put a horizontally-oriented speaker in the middle of your room, the way it interacts with room boundaries is necessarily going to make it sound a little different than the Left and Right speakers.
So, probably the "ideal" thing for you would be to get another M80ti for your center. I know in MY house, that would NOT work, placement-wise.
Everything I've heard about the VP180 suggests that it is a meaningful improvement over the VP150. I wouldn't hesitate to combine it with ti series towers. I will almost certainly do so myself someday. Timing and budget just aren't right for me at the moment.
