Is there a simple way to convert .hma files to .mp3 format?
Converting Sony HI-MD Audio Files directly to MP3 Audio Files (.hma to .mp3 conversion) should be possible, even though your options are quite limited.
Use the Sony MP3 Conversion Tool, which allow users to convert HMA (ATRAC) files to MP3 format.
Converts ATRAC format audio files in your computer to MP3 format audio files.