I have a Walkabout, and I just picked up an M-Pulse 600. I'm trying to decide which to keep. On my Walkabout, the pre starts saturating and breaking up at around 12:00, and there's plenty of grit past there. On the M-Pulse, I can't get it to distort until the knob is maxed out, and even then it's pretty slight. Are the preamps on these two amps different? I thought they would be the same. Could the difference just be in the tubes?