Looks like you might need to use DVRFlash
. I don't have a Pioneer drive myself but I'm sure there are people here who have as well as used the hacked firmwares on that page too. Just scroll up for the rest of the info on the page.
Of course the main RPC1 page shows that there is a MacOSX flasher...that one is probably a stock Pioneer firmware with an OSX-compatible flasher built-in. Don't know much about OSX stuff either so YMMV... http://forum.rpc1.org/dl_firmware.php?category=4&manufactor=25
Also make sure that your drive is a real Pioneer DVR-108 and not a re-badged OEM one from Sony, Medion, etc.