I think this is probably your best bet, although I gotta admit I'm not familiar with the "genres". In my opinion, at some point, you run out of room to just add more gain and need to look for something else to get heavier or more grind. I think that a stupidly big amp setup is tough to beat. Even without that, too small an amp isn't going to sound right no matter how many pedals you throw in front.
Assuming that cheap means a huge amp isn't going to happen I'd start thinking about ways to mess with the textures of the distortion sound I already kinda liked. I think some messing with an EQ (maybe in parallell chains), or something to add a few wierd or dissonant overtones/harmonics would be my next thought if EQ is too boring.
The way you talk about playing fast, I figure that super high gain fuzz or square wave style pedals aren't necessarily the way to go. Much as there's a place for it and they're fun, if it was me I'd try to stick with something that might be a bit more dynamic. I find that a square wave-y fuzz or a big boost into a dirt box just kinda powers out and work better when you're not playing super fast.
If I wasn't going to biamp I'd be highpassing one channel and blasting a distortion with it. Get the bass out before you get your high gain, aggressive tone. Lots of mids, filter out the harsh treble to keep it from shredding your eardrums. Then with the other channel either keep it clean-ish or get something with beefy lows and low mids (VT bass/blueberry/etc) and subtler distortion.
so my setup might be...
Bass> LS-2.
LS-2a> Rat or rangemaster+distortion or etc
LS-2b> VTbass with lots of lowpass.
LS-2 out>amp.
Or, get a guitarist to fill the gap.
