I just bought a used Ampeg SVT-4 Pro. My problem isn't volume, as has been discussed several times before. It has more to do with over-driving this thing. Using various basses, including an active Washburn Force 4, I need to crank the gain to max, use a pick, and drive those strings for all they're worth to even start to get the grrrrrrr sound I love so much. It's just too damn clean. With my Marshall 4210 combo, 1/4 gain rides pretty clean, with a nice increase at 1/2, and full sweep giving me off-the-chart distortion. These two amps seem to be polar opposites in the drive dept, and I'm looking for something in-between. So I'm wondering what my options are using the Ampeg: replace the preamp tubes with something gnarlier, and if so, which ones. add a boost box before the input. or just get the OD box(es) of my choice - currently digging the SansAmp Oxford. other ideas? Thanks!