I'm dumbfounded by the lack of bass problem.
My Sound Pro AT831s (Schwilly used Spargey's 831s, not mine this time) always worked fine for Schwilly with my AD-20. So did Spargey's at some local bands and King Crimson. Bass galore. Sound Pro battery box bass roll-off set at "69" and "95" Hz worked just right. 10k ohms impedance on the AD-20 input.
The MP-2 worked fine with my DPA 4061s and MPS-6010 at Primus. I chose to use the JK Labs homebrew roll-off on my DPA MPS-6010 instead of the MP-2's - I was more familiar with the DPA box and decided not to mess. Worked perfectly... so I seriously doubt that the lack of bass (most evident in the first band, Moonspell) is due to some malfucktion in the MP-2.
There is a SEVERE lack of bass throughout the first band's set, and the entire show, for that matter. It sounds like ass because of that, and they rocked, so this needs to be figured out for next time.
Maybe this lack of bass is due to the combination of the SP-CMC-whatevers (AT831s) > SP-regular battery box, who knows those #s anyway > MP-2. Hell if I know.
Armen