Ok, well now that I have a minute, I may as well just write my 'review' now.
Basically, the Foglifters do exactly what Rob says they do: the lows are more focused, and the feel is improved. The highs are more airy and open (less shrill), and the sweep of the presence pot feels a bit more reserved, natural. This is probably about as succinct as I can be here.
Now, the biggest downside to all this is the fact that both PCBs must be removed and sent in for modification. You actually have to remove the front panel to accomplish this (which you'd still have to do if they were drop-in replacements anyway). Having done it once, it wouldn't be a problem, but it was a huge annoyance at the time, probably enhanced by the fact that I really do not enjoy tinkering with small parts to begin with. That said though, it was worth every minute.
Bottom line, my honest opinion is that this is an essential upgrade for these amps.
Hope that helps - any more specific questions, please ask away.
