I made a demo on the metal muff, it didn't turn out so well. I'm still learning how to tweak it with the RG100ES. I've listen to other metal muffs on youtube and put mine to shame. So I'll probably tweak some more and remake a new video. lol
http://www.youtube.com/watch?v=oUifX8k_-Ck
And the second video is of a Guyatone MMX Metal Monster. It's loaded with a 12ax7 Sovtek. Pure metal pedal and sound phenomenal through the Randall RG100ES.
http://www.youtube.com/watch?v=ybEssXFNVqM
Enjoy!