I need to be careful here, as there are strict rules on this forum about linking to roms, but there is a torrent of already converted roms on a popular torrent website whose name is a bit like the buccaneer harbor.
That said, as a Mac user, I had the same troubles you did. I have found that a boot camp partition is a necessity when it comes to this kind of thing. GBATA, Dingoo Converter, etc... all Windows only. You'll want to find yourself a copy of Windows.