You can use distortion and reverb at the same time, as there is a dedicated reverb-processor AND a separate EFX-processor on the XP-30. The XP's have three processors: EFX, reverb and chorus. Each of these processor can only have one setting. This means that if the EFX is making distortion, you can not at the same time have rotary speaker. This is because the EFX is the only processor able to create any of these effects, and it can only have one setting at any given time.
However, you can adjust how much each channel will send to the different processors, just as in a conventional mixer.
Hope this answers your question..
Stig