Visualrocker, why are you so reluctant to turn the master volume on the triaxis up. I always look at my gear kind of like a faucet. If you turn the knob just a little only a little water makes it out. If I have a garden hose attached to the faucet, I only get a depressing dribble of water out the nozzle. If I want the nozzle to really shoot water out the hose, I have to go to the faucet and crank it.
I would advise having the levels coming out of the triaxis as hot as possible while keeping your cleans clean. Then adjust the volume of the 2:90 to your playing levels. If the 2:90's knob is a little too touchy, then start pulling back on the triaxis's volume.
But on the other hand of your looking for kind of a Marshall type sound, the triaxis is going to fight you the whole way. You might think about getting another pre and plug that into channel b, then use an a/b pedal to switch between the two if the triaxis just isn't providing you the sound you want.
As for the vetta comment, the vetta is a really cool and versatile amp. It'll give you nearly any tone you could want. In the hands of someone who's willing to tackle it's options and tone sculpting abilities it's versatility is unmatchable. But given the fact that 18&life only needs two sounds out of his triaxis he probably wasn't able to make it through the vetta's manual.
