Hi Bayne,
I'd have to agree with Adrian on your not getting much improvement from the VP150 over the 100. If you like the idea of the M5HPs as your left and right mains, perhaps you should use one of your M3s as a center channel. It's far more neutral than the VP100 or the 150, and should blend smoothly with the M5s. Note that I've never heard the M5s, but I expect they are excellent. And you already know what a great natural-sounding center channel can sound like, since you already own the VP160.
Note also that during my years working for Axiom, I never liked the VP100, and the VP150 was what I'd call "adequate" at best. I always encouraged Ian to develop a no-compromise center channel, which the VP160 and VP180 certainly are.
Regards,
Alan
