This is a longshot, but maybe you could try enabling automatic USB mode? Connect the Sage to the PC that works, then edit Kobo eReader.conf to add:
Code:
[DeveloperSettings]
AutoUsbGadget=true
and then save it. This will bypass the USB prompt and automatically connect when you plug the Sage in. Now try on the Mac again to see if you can get farther now that it won't freeze on the USB prompt.