The JSX is the best amp i've got and the best amp i've tried period. Superb cleans, the second channel has more mids, a bit more 6505'ish but without ugly treble. The third channel has some more gain and is a bit more scooped. You don't really need a maxon od808 boost, this is a tight sucker. But if you want a bit thicker lowmids then of course the 808 will do the trick.
You can check out my Start a fire mix on my website, its JSX on the rythm.