I've tried this before the results were horrendous
If you want something better from the Triaxis thru a combo, make sure your amp has a preamp in input to by pass the amp's own preamp.
Seriously putting the triaxis thru a combo's input...it really sounds bad.
You don't really need to get a simul class 2.90, any other reasonably good powamp will do. Why not a mesa 20/20 or 50/50. As for cabs...well to me they're just speakers (Yeah Right!).
I've taken a triaxis for a spin for a month or so on loan from a friend. And I felt it does not suit my needs and useage, to get that true distortion tone, you gotta turn it up really loud! A little too loud for my humble sized apartment.
But if it's dual rectifier
tone you're looking for, why not try out one of the mesa combos? The single rectifier series...rectoverb is a pretty good buy as well. Tremoverbs, Mark IVs...*drool!*
Good luck man!