Hi, I bought the PS Audio M700's to run my big Kef Reference 5 speakers. I was really impressed with them given their size and weight. So impressed that I very quickly considered the M1200's as an upgrade. In the end I jumped straight to the BHK 300's which I bought used. There is a big difference, as you would expect but I was surprised at how warm sounding they are. I say this because the BHK's are fitted with Tubes on the Input stage as are the 1200's. I have not heard the 1200's personally, but I suspect they will offer a warmer, smoother sound than the 700's, not to mention lots more power.
I only have good things to say reference P S Audio so, If you do get them, I'm sure you won't regret it.