I tried to find hidden sound volume settings to see if that'll work to fix things. C:\Program Files\HTC\Aces High II\settings (* your installation folder may vary) holds configuration files, and the file "sndgrp.cfg" appears to hold the slidebar values in the screenshot that gyrene81 posted. Also found in that folder is a "sounds.cfg" file, but unfortunately changing the values in that .cfg file seems to do nothing. I even changed the values, recorded the audio on fraps, changed again, fraps'd, etc, and then listened to the fraps recordings back to back to make sure I wasn't fooling myself. I'm guessing that is now a legacy file, no longer used.
Something for the "advanced user only" would be useful, even if you can't implement it right away, HTC.