Perhaps, a tube amp or something sound similar would be a way to go. It seems to me that Dan himself tuned them to sound best with a tube amp. At this moment, Lyr 3 seems a good option for a price. Single ended, but very powerful.
I've been using my AFO's now for a couple of weeks on a Lyr3 + Bimby stack, and EQ'd to the harman curve on JRiver-EasyQ. It really is a wonderful listening experience, excellent bass response, very nice clarity in the mids, great imaging and air. The only areas I can't quite get under control is a tiny bit too much sibilance in some highs, and not the best bass control/tightness, but this I think is just inherent in the design. Really liking these!