I have had a pair of ADG Class D monoblocks in my system. My preamp is an Audio Research Reference 6SE. I was really impressed at the sound for the money.
One thing, I will say, that when you take out one piece of equipment with a very synergistic system... that one piece tends to sound as good as it ever could. So I had all Audio Research electronics a substituted just the amp.
But sounded great for the ~$9K