Wow, thats quite a strange mixed bag you got there.
I'm guessing it was the pre-amp causing this as it disappears after you removed it from the chain. Maybe something faulty inside.
Anyone else have any ideas?
Agreed. I also think it's probably not the mics as it's a stereo problem (but something could have zapped both of them I suppose). I'd suggest the power supply side in the preamp has busted?
Question, can you plug the mics directly into the R-09 mic inputs (turn plugin power on from the menus). Test it that way.
Actually looking at this pic of the mics I see you can...I'd lose the pre-amp and see how you go.
digifish