If you run M22ti(s) as your l/r mains, which would be preferable, sonically, as a cc, between a 3rd M22 (mounted vertically) and a VP150?

It depends on who you ask.

Most people need the horizontal speaker to place on top of their tv's.

Sonically, a 3rd vertical M22 is the your best option since it would match perfectly. Whether or not that's aesthetically pleasing or physically possible given your A/V furniture is another question.

Thanks for the quick response. In this case neither aesthetics nor placement are major issues. I'm getting a big ol' RPTV and there'll be about 22 inches of room from floor level to screen. The M22s are 20' high. Just thinking about the floor option as opposed to the top-of-set mount.

That would actually look pretty good, IMO. I'd consider putting a wedge of some sort under the front on the M22 so the tweeter points straight at your head, though. It'll sound better, especially if you've got a coffee table in between you and the screen.

LF, that should work well. There's no problem with having the M22 right on the floor, possibly tilted back slightly, as Peter mentioned. Watch the distance calibrations so that the center doesn't come out closer than the mains.

I was thinking a pair of M22s, on their sides, head-to-head, but sitting on wedges to angle them toward the A+ sitting/viewing position might be a nice center channel set up. Might go well with 4 ohm M80s.

Yes, 2x6 that would be interesting, but if by head-to-head you meant tweeter to tweeter I would think that the opposite arrangement, i.e. TMMMMT, might be better, creating in effect a super VP150.