I just grabbed a Boss DS-1 to put in front of my 2 channel Dual Rec. After also retubing the amp (Tungsol in V1, and new Mesa 12ax7 in V2-V5, Tungsol 6L6s, and JJ Rectifier tubes), the amp has tightened up considerably, even without a boost. But the DS-1 pushes it up to a different level.
I picked the DS-1 over all the tubescreamer circuits mainly because its 92% the same circuit, but with an asymmetrical diode clipping section, which i feel gives my palm muting style a bit more organic feel. sounds more like overdriving tubes versus the more digital sounding drive that i think the various tubescreamer circuits produce. just my opinion though.
DS-1 pedal settings: Level about 2-3 o'clock, Drive just a notch above zero, Tone about 11 o'clock to warm the midrange up a bit.
Hope a different opinion helps.
either way, enjoy your amp