is that theyre [Rectifier amps] using a hybrid transistor/[doide?]/tube preamp distortion, then the [rectifier tube's'], output tubes [and speakers] have thier way wiith the signal...one of those 'get that and you got 'IT' deals...not to say it can't be retro-replicated...there's probly a # of competitors amps [Crate? etc] that attempt it.
I also like the Boss Metal Zone. I don't play metal, but I like the tones I can get out of it. The EQ's really help you to shape the sound. I think it's great for lead guitar riff's and stuff. Nice and thick.