Your problem is very specific and I don't know the reason, but here are some thoughts:
- i'm always using the DT25 reverb , not the pod reverb, you could try and see
- rather than tweaking GuitarZ , there is a pad switch on the pod, designed to tame high output / active pickups , try it
- in the end try to lower the preamp volume , or use the mixer to go down a few db, though this might modify your tone a bit
Also after trying a few attenuators, never been convinced, I have bought a reignmaker eminence speaker that has technology to reduce spl by up to -8 dB , and it works great, no tone loss at all.
Only drawback is it didn't fit in my DT25 combo, I had to switch to head + cab stack
http://www.eminence.com/speakers/speaker-detail/?model=Reignmaker