Well, not really. I saw those boxes. The ISO box essentially provides a high quality line out straight from the path between the amp and cab. The other box on that page, the MiniMixII, would probably be of more use to me since my vintage amps have rudimentary serial loops from the seventies. That MiniMix is a pretty cool idea.
Basically, I just want to use my G-Major with my vintage amps. I'd like to do it in the signal path between my guitar and amp, but apparently it isn't recommended to use the G-Major this way, so I have to figure out another way...
Thanks for the help though!