Nice camera. This is when a 35mm adapter does make sense.. you have a multi $k investment in a camera, for another $k or so you can have great look and features.
I only have a consumer grade canon HD cam.
Iv used used my letus on a Panasonic HMC150, much more more pro the my cam, and the shots are BRILLIANT.
With the JVC that would be a nice rig. Some of the pro cameras benefit from a specially acromat, check the letus site for details, though on my cursory investigation I didnt see your camera as one that needs the special acromat.
If your going PL mount, and know why thats cool, then your out of my league.
Your already committed to multi thousands dolor lens sets.. me, I run old canon FD lenses, $10 pawn shop specials up to my pride and joy f1.4 50mm ($60) so ....
You might consider the Letus ultimate over the extreme.. ... im posting incomplete because my satellite connection is acting up..