Hi,
You can adjust the amplitude of the individual notes using a wave editing program (a good free one is Wavosaur). Go into the folder that contains the .organ file and locate the subfolder for the PosHautbois8. The notes in that subfolder are of the Hautbois rank and are numbered following the standard MIDI Note numbering (so middle C is 060-C.wav). Once you have adjusted the volume/amplitude in the wave file you will need to exit and reload in GrandOrgue/HW3 to hear the difference. If you don't feel comfortable doing the editing, just let me know & I'll I'll do the adjustments and send them to you for testing
GrahamG