It's not so much that the two amps will "cancel" each other, it's that they'd provide too much of the same sound and get REALLY muddy so you wouldn't be as clear on separate parts. If you BOTH set your amps the same way it will be impossible to keep the sounds separate. You can both use the same amp, but you'd need to make sure your settings for EQ and everything else are completely different. Even at that, some of the inherent tonal quality will remain and it will still not be as clear as if you have two different amps.

Amps are a personal choice and you should listen to a number of different ones. From the studio perspective we see all kinds of amps in our space. Marshall's are quite popular and we have one or two a week. Peavey's sound the worst in the studio, (at least they do in ours,) but that's in the studio. Live can be a completely different story. We've had groups in the studio use the same head and cab for lead and rhythm. It sounds like ass. They insist on doing it though. (We record a clean track and then reamp one of the guitars through different amps after they've left. When they hear the difference, they begin to realize the error of their ways.)

So you have part of your answer. Having different amps is a good thing! Take your time and try EVERYTHING no matter how silly it might seem. Then buy the amp that makes you grin.

right on, i'll just start playing everything under the sun i guess. based on your advice i think i'll definitely stay away from getting a mesa as well. thanks man

If you don't want to go Mesa, I would say Marshall is the way to go.

I hate everything peavey... bad experience once and I just won't let it go.

I use a marshall TSL and I love it. Some people tell me how much greater the DSL is. I didn't find it to be any greater, but you might. My amp kicks ass, is loud enough to blow my head off, and I can get tons of different sounds out of it.

The new Traynor head is really awesome sounding, and it's like $900. I dont remember the name of it, but its big and silvery with tons of knobs. They finally looked after the rock and metal crowd with that one.

Having a Mesa would more than likely be fine if you kept your settings seperate, and I assuem you play a different guitar. I generally keep my gain settings low even when I'm playing heavy stuff so I get more definition per note - in a two guitar situation with one being more saturated it sounds pretty killer.

yeah i'd have to say marshall is the way i'm leaning. i really don't like peaveys either. i'll definitely check out the TSL and DSL's, that sounds like a good option.