Are you connected to the printer with anything other than USB? I know that had caused some problems for me in the past.
Look in your HD/library/printers/qtr/quadtone/quad7800 folder to see if your .quad profiles are in there. You might just be able to drag the profiles you made in windows GUI into that folder (not the one with the install script), then run the install script in the applications/quadtonerip/profiles/7800 folder. It should load the .quad files from the folder in /library even if you don't have them in your /profiles in the quad tone rip application folder.
I can check tomorrow when I get up to the studio to see if dropping the .quad like that will allow you to then print with them.
The .qdif is just a designation for the windows side of things (I'm not sure why) but it is just a .txt file as far as osx is concerned (although trying to open it will launch curve view). If you just drag .qdif file to text edit in the doc, or right/control click then open with text edit, it will then open like a normal plain text file. You can then try to rename and save as .txt in the application/qtr/profile/7800 then run the install script.
If it doesn't give you an error and the .quad files are in the folder in /library but it still isn't showing up in the QTR print dialog then I'm not sure what it could be.