Not a 'tube amp' by most standards - just one in the preamp, and it may even be a starved-plate at that, so I wouldn't gamble on that being the best thing. Plus, it's a modeler built around a tube that was originally picked for price (NOT tone)... abandon hope, all who enter here with the impression that they're getting a Rec.
Ok, I'm really just a sarcastic, elitist bastard... ignore that. It takes a bit of work to get a good sound out of it - it's not doing Ride The Lightning, kid, sorry... but it can be pretty slamming if you spend a good bit of time and your pickups don't suck. Generally, modeling amps at that price do not like other distortion coming in to their distortion channels, so I wouldn't boost it. You might, however, appreciate some pedal distortion - Danelectro Fab Metal (not bad for the price, but unless you feel like soldering components the size of a pen's point you're not modding it), Ibanez SM-7 (two 4558 chips - the same chips used in 'classic' Tube Screamers - set up for great sounds; a bit more gain than I like using in most cases but it's fun to play with... and it's fairly mod-friendly, if five separate PCBs and multiple gain/clip stages don't scare your balls back into your ribcage), Boss DS-1 with TONS of mods (pending the outcome of my newest toy - ordered one of these on an impulse-buy and I'm waiting for it to come in - I might be able to mod something for you), or even maybe a DIY box if you feel like putting something together.
I can't remember what your gear is, but I have little doubt that a beast like a Hellraiser will help your case (unless the 707s decide that they want to rape your poor little Valvetronix in every hole they find and a few that aren't there yet... in which case you needed an upgrade anyway; I've heard of bad things happening when a modeling system expects Bud Light and you shove Guinness down its throat); wouldn't recommend buying more than, say, $60 of new gear until you've seen whether you're happier with a better guitar.
One thing to remember... if you're at 2:00 on the model I'm assuming you're using (US HiGain) I'd say that you might be saturating things too much. Take this with a grain of salt, keeping in mind that I like having a range from 'mild breakup' with light picking to the clip I posted on the other thread (without changing anything but attack), but I'd say that you'll like the amp better if you let it breathe a bit.
I wouldn't mod that, apart from maybe plunking down ten bucks for a Tesla 12AX7 just to see if that helps a little (I'm doubting that it will), but try one or two of the pedals above (hell, just order a Fab Metal for the hell of it, it's $15 and if you don't like it with that amp you can just carry it around and use it on a micro-amp for traveling) and see if you can get them hard enough. In a couple of weeks I'll put up clips from my modded DS-1 - I have two weeks left before summer classes, I've already set up Debian from scratch on the new computer, and I'm going to run out of books to read before too long, so I'll have plenty of things to play with and I might be able to set you up with a good mod.
Jeff