So I turned up presence all the way, and was playing with the damp parameter to see what effect it had on the presence range. I put damp to zero and... woah! It got louder, very bright and RAW. Cool tone! It is not mentioned in the manual or wiki manual, but searching here revealed that putting damp to zero completely disconnects the feedback loop in the power amp. What I didn't find is, since presence and depth work off the feedback loop, are these controls now shelving filters as when the power amp is disabled?