I am familiar with the JM, its big brother Dream Maker (nominee for best speaker name ever), and the stand-mount Rhythm Prizm. I saw empty Prisma cabinets too.
IMHO.....I think the RP has more of the sound-as-one wholeness and transparency associated with the best electrostatic loudspeakers. The prior models are in no way slouches in this regard, but the new models get you even closer to that sound effect.
I heard absolutely nothing preferred in the prior models. We used Duke's 5-piece sub technology with the RP, mandatory because of its size. The combination, even with a $200 receiver (I kid you not) was one of the best audio systems I've heard and I've been doing this and music for over 40 years.
Sooo...I have no experience with the full range performance of the larger Prisma. But Duke knows his um, "stuff" inside out and I'd bet my wife's cooking against yours (her meals are legendary in these parts) that the Prisma kicks you know what all the way through. My best understanding is the Prisma is the RP in a larger box and of course with different bass tuning.
The size of the sound, whallop, and unlimited SPL (I worked at the Sausalito Record Plant with 2x 15" JBL and huge horn lens in each of four corners, biamped with 300Wpc...you ran and hide when Sly Stone entered the control room) are just out of this world and unknown unless you completely uncork your check book and get something about 6x larger.......You would have been floored hearing Rush at live levels on that system, in a huge room completely open on one side. Owing Duke's speakers makes you one of the less than 1% of audiophiles with personal experience hearing the absence of thermal compression and the absence of leading edge transient compression at live levels. I still miss it. In fact, it's ruined me to the point of needing a new amp because my speakers are only about 88 dB sensitivity.
Now please stop bothering Duke so he can return to his huge back orders of his smash-hit Thunderchild compact bass/cello enclosure!