The latest version of General MIDI Player (v1.3) was just approved by Apple and should be available in the App Store shortly. Changes:
* Added new Reverb control
* Overall volume level again increased - using a different approach under the hood, should make future enhancements easier too
* Can now output audio through any CoreAudio output device
* Now complies with Apple's sandbox guidelines - I wrestled with this for a while, and hopefully have it all sorted now! Again, should make future updates easier.
Thanks for the support and the ongoing feedback!