Hi there. Big fan of my GK800RB. I've just about wore it out, if that's possible. I recently bought a cherry TF 550B, with 'the switch.' Nice amp. Now, one of the things I love about my 800 RB is that while it doesn't go super deep it retains a very tight low end. But the main thing I love about it is the upper mid range /lower treble response. It just has loads of character there, bright without being irritating particularly with the boost set to approximately 2 o'clock. It's the 'upper harmonic complexity' thing it does, which is just sex IMO. Enter the 550B. This amazing amp goes deeper but in a very controlled, authoritative way, and frankly I'm loving it. It never gets woofy or stupid. Just killer down there. Way superior to the GK in controllable, extended yet solid low end. It's ability to control the low end is inspiring. BUT it completely lacks the upper mid/lower treble 'push' and 'grind' that the GK excels at, which again is something I really, really love and need. It's not a matter of EQ-the TF has plenty and it's excellent. But it doesn't "get me there" like the GK does. I need that "grind" that the GK does, with the tight, extended low end of the TF. Huh. Hmmm. Anybody know of a good compromise?