Thanks guys. Browlett; I don't know enough about this thing to answer some of your questions. I'll get back with you. I just expected to be blown away by this thing. I know it's gonna happen if I just be patient. I'll have more time to play with it tomorrow night and Saturday. I just hooked it up today.
It'll definitely take more work than just hooking it up and going at it. Make sure you've got all the I/O stuff set up properly first or you'll just drive yourself nuts trying to fix it with tweaking. If you didn't buy it new, check other things like the global EQ too.
Once you've got it set up properly, the best thing to do (aside from browsing the presets if you want to get an idea of just what the thing can do FX-wise) is to just blank out a patch and start with the basics. In your case, running the ART through a guitar cab, I'd say basically an amp block (w/poweramp sim) and that's it.
A "good metal sound" is fairly broad though, so it's hard to say which amp to start with. I used to be a Mark series nut, so that's where I started. More recently though I've been using the Uber and thoroughly enjoying it. I also like the Shiva, although it's not really for tight metal stuff unless you're doing other things to tighten it up. That said, I've done metal with an unreasonably cranked JCM800, the Mark IV stuff, Uber, Cornford, Diezel, Shiva, Shiva + Fuzz Face, etc. etc. Plenty of options, just depends on what kind of sound and feel you want.
I've been running mine just through monitors ever since I got it (well, I plugged it into a tube poweramp and cab when I first got it, but was selling that stuff off anyway) and suffer no "digital harshness" or anything of the sort.