Originally Posted by Silverwulf
Aside from what Dave said (which is the best advice I could give you, too)...
1.) I'm a pretty new EL34 user so I'm going off little more than first impressions here, but it seems like it's a better "hard rock" amp with ELs and a better "metal" amp with 6L6s. The later are deeper and clearer in the low end and a bit smoother, the former aren't as tight in the low end (but not in an unappealing way), a bit rawer in the highs, and a little more focused in the midrange. Think, oh, hell, I'm trying to think of a band that has a rhythm sound that sounds a bit like an EL-driven Recto, and I'm striking out. A LITTLE like Porcupine Tree's In Absentia tone, but deeper in the low/low mids and with that Recto midrange, boosted up a bit. It's a cool sound and it works for what I'm doing, I think, but the Petrucci school of tone, you'll want 6L6s (and this amp nails it). For EL34s, I've got Groove Tubes EL34Ms in there now, which I like so far - Matt swears by the SED Winged-Cs, so that'll probably be the next set I try.
2.) Channel 4 modern, no questions, for heavy rhythm. For leads, definitely channel 3, but I go back and forth between Vintage and Modern - they really aren't THAT different sounding, surprisingly. Modern's a hair hotter and more saturated, Vintage is a little more open. Personal taste, really.
3.) Haven't experimented widely, but my TS9ovChaos is pretty sweet.
4.) Well, it's a Recto - you have a pretty good idea how to dial one in. It seems less "quirky" than other Rectos I've played - I have no basis to state this, but I feel like Mesa may have tweaked the EQ section a little to make it respond a bit more predictably... Just fire it up and have fun. Oh, and crack open a beer first.