Michael,
My reaction when I switched from my old amp? Surprisingly hard to do, because I'm setting up a new system in a new room with new speakers and new electronics! I think it's a very, very good amp that doesn't have quite the grunt of my old Bryston 14B (at 3 or 4 times the power). However, the Fet Valve 400R does have (more important to me) excellent tonality and still very good control. It has better timbre reproduction, to my ears, than the Marsh Sound Design A400S I used in the interim.
A professional mastering engineer was over to hear the system yesterday, and I played a Norah Jones cut for him that I'd heard at his shop. He looked at me, a little befuddled, and said it was really nice. Then: "I've always thought there was something wrong with the vocals on that album, but there was NOTHING wrong with it right now." He thought it was probably an $8k amp.
Hope that helps.
Mike