JP6 and RGA are totally different guitars. The necks on the MM are tiny, very thin and narrow, and the pickups on the jp are much clearer and more 'traditional' sounding, even though the crunch lab is seriously hot.
Piezo doesn't mean good cleans, I HATED the Piezo pickup on my JP. Great through an acoustic amp or a JC120, but it sounded really awful through my Roadster. However, the middle position on the pickup selector (where it splits both pickups) sounded excellent for cleans.
The JP6 is easier to buy used, which I recommend, the prices went up recently and are now insane (here, about £2200 for a standard model) when a couple of years ago they were 1k less, so the people selling them used I think are just glad to get their money back, so they can be had for good money, and they're great value.
There have been some very unique limited colours in the past too, I really wanted a Lava Pearl, but went with a Graphite pearl.
I hope I'm misreading this, but if you expected to run the piezo by itself through a Roadster & expected anything pleasing to tickle you ears, you shouldn't be surprised that you didn't. Perhaps when blended with the magnetic pickups, but never alone. Those piezo elements are truly meant to be run into a processor/P.A. and not through an electric guitar amp. Unless it's a JC120, it's gonna sound awful.
That being said, the piezo on my Parker sounds great
through my Zoom A2 and into the board and on out to the P.A. system. We're talking pretty darn good. Not Taylor acoustic good, but more than passable for acoustic sounds from an electric.
Regarding the guitars: If you've got the money for either, I'd go with the Music Man. I love Ibanez, but the JP6 I tried out nearly played itself. It had a feeling of quality that was on par with or slightly better than my Jem. Also, it's got pretty hot DiMarzios already in there. I don't care if they're passive or active, but anything that comes stock on Ibanez that is made
by Ibanez is an inferior pickup & should be changed out by anyone serious about their guitar. Pickups more than anything are, IMO, Ibanez' Achilles heel. Paying over a grand for an Ibanez without
DiMarzio's is a crime....