I was a big fan of Satriani in my 'early years', used to love his tone.
So I bought the 'other' Satriani amp, the Marshall 30th anniversary. The one he used live for years, since the mid-90s or so. He originally got them as loaners from Marshall when his own JCM800 and JCM900 were stolen.
Funny enough, even though it's a 3-channel amp with a lead channel that has an insane amount of gain, he still chose to use his Boss DS-1 pedal, and run it through the clean channel.
Because of problems with the amps (they break down quite regularly when on the road, and because they're such complicated hi-tech amps, not even Marshall themselves could repair them back to their original state), Satriani decided that he wanted a new amp... one that could easily be repaired or replaced. Marshall wasn't interested in taking the 30th Anniversary back into production, not even as a signature model... so Satriani eventually ended up with Peavey, and this is the result.
From what I understood, Satriani still uses the DS-1 over the clean channel... The clean channel was actually created more or less like the 30th Anniversary, so that it would respond nicely to such pedals.
I suppose Satriani himself doesn't use the ultra channel either.
I spoke to another owner of a 30th Anniversary, and he said he never used the lead channel at first, because he didn't really know what to do with it... He played lead over the crunch channel, which also has plenty of gain, more or less like you described... And he had set up the lead channel for rhythm aswell.
I personally use a slight treble boost on my lead channel. This gives it a smooth and articulate lead tone, without requiring much gain (I generally have it set to 4, which gives me total saturation). It's quite boogie-like, really... just more focused mids. And it responds excellently on picking and rolling down the volume. Reminds me a bit of Steve Lukather or Neal Schon.
Anyway, I suppose I should check out the Peavey JSX sometime. Personally I think Satriani's old tone, from around the time of Flying In A Blue Dream, up to the first G3-tour, is the best tone he's had... Nice and smooth.
But I'm not sure if it's because of the Peavey he uses now, or because he just changed his tone period... I suppose the Peavey is versatile and good enough to also give you those older Satch tones.
Lovely guitar btw... I love figured tops and all... Guitars are wood, and that should show
I have an Amber sunburst RG570CT myself. And an Epi Les Paul... all figured maple tops.