Hi Brian, I ran the X 150 and X 600 on Duetta Signatures for some time. I don't think they are worth the price. There are others that have both speakers, but I don't know what amps they are using.
The 350 does run at class A for the first 100 watts. I had another fully class A amp for a time on the Duettas, and that was just great. It filled the stage with beautiful music.