Doesn't creating a file in the .is_audio_player in the MyDocs folder enough for it to be picked up as a audio player for music stored on the N900 internal memory?

The content of .is_audio_player would be somewhat like the following:

audio_folders=Music/
folder_depth=2
output_formats=audio/ogg,audio/x-ms-wma,audio/mpeg,audio/wav,audio/flac,audio/mp3

If the music is stored on the removable drive, put the .is_audio_file into the root of the sd card.