Sorry, a little bit off topic but...
Just curious Dewdman, have you tried re-naming your SouldFont (or DLS file) and put it in place of the default "gs_instruments.dls" file ?
I was wondering if that fixed the MIDI low volume problem that Apple has had since 10.6 ?
If you were not aware there was a bug introduced in 10.6 which cut the MIDI output volume drastically.
I am on 10.7 and the problem still exists, and I am told it is still not fixed in 10.8.
Google search for "OS X low MIDI volume" for more info.
Myself I went back to using my external SoundCanvas, since Apple hasn't fixed this yet, and I got tired of updating all my existing work for the new MIDI volume settings.
If anyone interested in helping to get this issue resolved, I would suggest filing a bug report with Apple.
I know I have reported this several times, with each OS update, maybe if enough people report it they will fix it.
https://bugreport.apple.com/cgi-bin/WebObjects/RadarWeb.woa/wa/signInSorry about going OT, but I was hoping this may be a workaround for the low volume problem.
- Jay