Hi gtononi,
I use ARC2 with JR every day on both Mac and Windows and never had problems.
When you install ARC2 on Mac, usually both the VST and the Audio Unit (Components) are installed. You simply have to add the VST ARC2 plug-in in the DSPStudio of JR, have it checked to enable it and then from the plug-in window choose your filter in the Measurement menu.
The Measurement files, those with the .arc2 extension, usually are stored in ~/Documents/IK Multimedia/ARC System 2/Measurements: that way they are available from within the plug-in itself in the Measurement menu.
Those measurement files are available for both plug-in versions, VST and AU.
Hope this might help you…
Regards
arin