Hmmm... Horizontal L/R mains you say eh? Now that would be an original set-up!
There is a picture posted here on the forum (can’t remember where) of somebody, I think in California who set up 3 VP150s across the front.
I am very interested in how the VP180 sounds vertically. I can’t see why it wouldn’t sound as good or even better (often horizontal centers arrayed vertically have better horizontal dispersion). Assuming it does match the M80s well (can’t imagine why it won’t) then being able to have 3 VP180s up front arrayed either vertically, horizontally or a combination of both opens up some interesting placement possibilities and tweaking opportunities.
I’ve already toyed with the idea of using the fabrication shop at work to make 3 stands that would allow the VP180 to rotate 90 degrees from horizontal to vertical. I could have them arrayed vertically for music and have the center or all three turned horizontally for movies. Just so happens that three of them will fit horizontally under my screen with just enough room to spare to allow them to spin.
Also with symmetrical driver placement I think the VP180 might even work better than the M80s on the sides of the screen elevated up off the ground. This would give the option like some have done with the on/in-wall speakers of having the screen framed with VP180s.
Lots of interesting possibilities with this design IMO.