Mostly because its a flimsy, thin preamp signal. It's going to be hard to get a good sound with just that (unless that's the sound you're going for.) Get yourself a real tube amp, a Shure SM57 and a decent Mic Preamp. There's no substitute for the interplay between saturated power tubes, a good speaker, the air and a mic. If you really like the flexibility of the Digitech, try using it as the preamp and send it into something with real power tubes. Crank the volume on the tube amp and you'll have the high gain mayhem you're looking for.