JJ 6v6's might be able to take the voltages the OTS will pump through them, but I wouldn't risk using them.
As far as tonal differences, in various amps, I've found that 6v6's are nowhere near as smooth sounding as 6L6's. In fact, the ragged nature of 6v6 overdrive is such that I can't stand using them for anything but early tweed Fenders.
The OTS has a great master volume, though, and in my experience, even with a 2x12 you should be able to get a good, low volume tone. Of course, your experience and mine are different, & I hope that you find a solution.
Thanks Bobgoblin,
All this stuff is so subjective. I was just looking to lower the power to turn up the amp.
JDOxO makes some interesting points about EL34's. Somebody had said on some thread a while ago that the power tubes didn't matter tonewise because of the preamp design - which was the first time I'd heard that about a guitar amp. That prompted my question.
Sounds like most people agree that power tubes make a tonal difference with the OTS?