I tried this amp with a Sennheiser HD650 and I was not very impressed (I remember I was not very impressed when I tried it a couple of years ago). Maybe the tubes were not in good condition).
But I did not try this amp as a speaker amp because I did not have them yet and neither an AKG K1000.
An advantage is that you can use the amp both as speaker amp and phone amp.
Anyway I shouldn't have started this review because it is more then 2 years ago since I owned it.
If I could I would delete this all.