Hello, I have never herd the original Genalex KT88s before, but all I have read indicates that they were quite the tube and if you can find them know and do not need a whole lot of them they are still one of the best HT88 tubes out.
I am running Audio Valve Challenger Mono Blocks which are auto biasing and can use EL34s, 6550 or KT88s. The wattage also changes with the type of output tube; the real negative side of this is that each amp takes (6) SIX tubes! When you are buying Genalex Gold Loin KT88s x 6 matched prs that is $550 BUCKS- well call me stupid but I dropped it for 12 bad boys and it was well worth it.
My amps came with Electro-Harmonix EL34s and putting these bad boys in was a huge improvement, starting with just plan more power and with power comes more AC needed to keep the room cool and believe you me it sure gets hotter now; then a much bigger sound stage more controlled deeper bass. The EL34s have a real luscious mid sound but the KT88s really rock, especially with Swing Jazz (Big Bad Voodoo Daddy) and Blues (Buddy Guy). Well worth the investment for me, however now I got curious and went and picked up 12 Ruby Tubes (6550s) and they are sounding pretty sweet (and over $250 less!)