I have the same amp and am using SED (Winged C) 6550's. I've been told by reliable sources that KT88's will give more extension on the highs, but not quite as nice in midrange. I haven't confirmed this. I also will soon be doing some 12AT7 tube rolling - which I hear is highly recommended. I'm using my amps to power the top end of Maggie 20.1's. What are you using yours for?
