This experience based upon the author having never biased any of the tubes.
05-27-07: Bartokfan
In my experience the KT88 tube is better for higher sensitivity speakers.
I only like KT90 and 6550's,. Well I'll hear the 6550 first time in 2 weeks.
Properly biasing tubes in a non-biasing tube amp means everything to the proper sound of the amplifier. Without having ever biased the tubes, one cannot legitimately comment on the highs, lows...or any other aspect of a tube's sound.
Sorry to beat this into the ground, but as long as you continue to share your experience listening to tubes in a tube amp which was never biased, then I will continue to caution new readers to take your comments with the appropriate perspective.
Frankly, I very much look forward to the first post you author after you have biased your amplifier. I suspect you will experience such a revelation in good sound that you will be physically shuddering with giddy enthusiasm.