The best RSR converter I've used is Dimension 3D's Runtime ZIP & Repair. Not only does it convert the RSR's to PNG's, but it also deletes them afterward. I just don't know if it works on the MAC system. Be aware, some very old content have made use of RSR's to store data. Those will not convert and will cause the program to quit prematurely. IIRC, there is an RSR file in the core Poser folder that shouldn't be touched.