Eric - I use Endorphin sometimes, and notice that when I adjust something the CPU usage meter climbs dramatically; it's clearly very demanding on processing power and I would think that's what causes your lockup. However after a couple of seconds it settles down again. The only suggestion I can make is to adjust the slider while playback is stopped. You might find that it pops etc when you hit play again for the first time, but works OK on a second play, once it's done all its little calculations.
Incidentally when I ran n-Track under W98, searching for effects while playing back would lock it up - much better with W2K.
