My band-mate has a Diablo head and Genz Benz 2x12 cab. I've never heard it's distortion though, as he uses it exclusively clean, to amplify his PODXT. And I have to say, that he gets the best sounds I have ever heard from a POD. DOn't know if it's because he has magic abilities, or if the Diablo just has the perfect combination of "whatever" for the POD, but it sounds OK, not great, but definately OK. I do know that in the past he has played around with the amp's distortion, and prefers the POD.
What I also know is that the transformers are tiddly for a 50/60 Watter, as the head is so light. For me, that would not bode well for long-term relibility or tone.
The amps are also not generally that well thought of on certain forums. The Black Pearl, is well-loved by many, but not the (much cheaper) Diablo.
So I can't really be of that much help, apart from my assumptions and relating other people's opinions. Sorry :?.