i havnt had any experience with the MPX1 but i know a few people who have.... The tones that come out of the MPX1 are great, but if you are going to use it for live situation with a midi controller, apparently it takes its time to switch between patches.. like 3 seconds or so.... i've also heard its hard to edit patches etc, but thats easily fixed by reading the manual..., I was considering an MPX1 but not buying one, because of the long time b/w swtiching presets...
Maybe consider a Tc Electronic G-Major or a Rocktron Xpression...

Maybe consider a Tc Electronic G-Major or a Rocktron Xpression...