.nkit.iso instead of .wbfs

I recently attempted to download a couple of ROMS and selected the WBFS option but I get the .nkit.iso version. This happened with both Call of Duty - Modern Warfare 3 and Donkey Kong Jungle Beat for Wii. If there is no WBFS format available is there a way on mac to convert these to WBFS? Thanks in advance!