They are an endorser of Mesa and have a video on the Mesa web site. They also play an endorsement deal guitar too. Washburn?? I was struggling to get some of that unusual sound. Ended up looking in a tab book. I think any old cruchy tone will do, the trick is in the unusual chordings Dave uses, lots of open strings and straight up weird fingerings, volume up and down, intensity of pick attack. Some of the same tools from Pixies or Nirvana. The tone is in the playing more with them IMO.
Good luck on your tone quest.