RawkSD apparently uses MIDI note 95 as the note used to chart double bass. If FoFiX could implement the use of this note, people would no longer need to distribute multiple MIDI files if they want to offer all difficulties and Expert+ drums. This would be how it could work:

1. FoFiX scans the MIDI to determine which difficulties to offer for the chart. If note 95 was encountered in PART DRUMS, and other Expert difficulty drum gems were found, FoFiX could offer Expert+ in addition to Expert.

2. When the chart is playing, note 95 (bass) would not be displayed or scored unless the Expert+ difficulty was selected.

Handling the tracking of the additional song difficulty in the scoring would probably be more difficult than the rest of this logic.

EOF and Phase Shift have just implemented this notation as Expert+. It would be a good feature for FoFiX to have, and shouldn't be very complicated to implement.