Thanks for all of the replies. The thing that makes most sense is that the mics are starved for power, and are brickwalling at loud shows. If they in fact require 6v, and the preamp is putting out less than 5v, and I only experience this at loud shows, I think that's it. Makes sense to me.
I really want to get back to a simpler rig, anyway....I don't record that often, and just want my mini-stereo terminated mics > battery box > recorder setup back. I am trying to see what Chris can do, maybe trade-in the mics and preamp for a set of his cards (he modified my mics and put mini-xlrs on 'em when I got the preamp).