How to increase the volume in the OSX PlaySoftMidi example.

I have an application written in C ++ and in the Qt cross platform library. It uses QuickTime on OSX to play midi events. On OSX 10.6, it works fine. On OSX 10.7 (Lion) the midi volume is very low. Increasing the volume of the system is not an option as the same application plays audio and also becomes too loud. I have searched several times for a fix, but found nothing useful. Apple released 10.7.3 and the issue still exists. Please note that it also exists in the system-supplied QuickTime player, so this is not just my code.

So, I changed the use of the DLS synthesizer interface using the Apple PlaySoftMIDI example. The result is exactly the same - very low volume for the Midi! I am guessing that I need to change the DLS synthesizer properties or the DefaultOutput components. My problem is that I cannot find a document that lists properties that apply to any of the AU unit components.