How to convert .rip audio files to .mp3 file format.
It should be possible to convert Hit'n'Mix Audio Mashup Files directly to MP3 Audio Files (.rip to .mp3 conversion). Your options might, however, be limited to using the original software.
Therefore, your best bet appears to be using the Hit'n'Mix software itself, as it should allow users to export its RIP mashups in MP3 format.