Anyone else caught this? If I try to open a MIDI file in QTX, it tells me I need to launch QT7. Why would Apple release a half-complete version of QTX?
If you want to get midi support back in Quicktime Go to http://apple.com/feedback and complain and keep complaining. Apple discontinued midi support in Mountain Lion. They don't listen to the forums, they do listen to feedback. Keep at them until they fix it.