I don't think many people have finished theirs yet. If things go well I should have mine powered on by next weekend... just waiting on some screws. I haven't heard the original KGSS though so I probably won't be much help. There were about 130 boards in the recent group buy, but most people bought 2+. I bought 1 on board and 1 off board because I wasn't sure which way I wanted to build it. I'm not planning to build the second one any time soon but others might be building multiple and selling the extras. I wouldn't go over there and ask if anyone will build you one though, you are liable to be run out of town.
There are several differences between the KGSS and KGSSHV. The most obvious is the +/-500 volt rails versus +/-350 on the KGSS. The difference is not just the voltage, the power supply is redesigned and should perform much better. In the amp the input jfets are updated to a lower noise part and a CCS is used in the output stage rather than a resistor. I believe those are the major changes, there may be some more that I am not aware of. You can read much more about it over at the other place.