I'm using a Musical Fidelity A308 with some F30's and am pretty happy with it. When I had M20's I was using an audio refinement complete integrated with pretty good success. I also owned the Pathos Classic One (version 2), although not while I had the M20's. I didn't have much good to say about it though. It just didn't seem to do anything right.
I would probably try a Musical Fidelity A300 if I were you.
I would probably try a Musical Fidelity A300 if I were you.