I still suspect the primary problem was a weak battery. Have you experienced the same distortion problem again since the original occurrence, using a fully charged fresh 9V in the preamp?
I've recorded another show 6 days ago and didn't experienced any distortion problem with a fresh battery and the CA-9100 set at ~10 o'clock.
But, I'm pretty sure the show was not as loud as the previous one as it was a semi-acoustic gig and I was standing further away from the speakers.
I taped 4 shows so far with the DPA's. The louder they were, the more brickwalled my tapes are.
the 4060's should be AOK when powered correctly, the specs for the 4061's are 144 dB SPL Before Clipping, 4060's are 134dB SPL
both of these are significantly high for LOUD shows like Melvins, Earth, Sunn, etc
again, for loud shows it is simplest to use your battery box rather than a preamp. A lot less can go wrong thataway!
I mainly record hard-rock bands like Rival Sons (think led Zeppelin) and do stack taping. It's loud.
I first taped with MM-HLSC-1's (Sennheiser MKE 2's - max SPL: 138dB) and had
to made them 4.7k modded to achieve non-brickwalled results.