How to export Audio in iReal Pro?

[dflat]

I have yet to use this feature, but exporting to audio does have an "AAC (M4A)" option. Where does this export to, if not to iTunes?

iOS - if you Save to Disk, it goes into iReal Pro's Documents folder; from iTunes on your computer you can access the audio files.
http://support.apple.com/kb/HT4094
(aside: for other apps, this can be a way to copy files into that app; for example you could copy PDFs from your computer into a PDF reader app, or video clips into (or out from) a video editing app.)

And I'm curious why you can export a file as AAC from the iOS version, but not from OSX.

.wav is higher quality - the computer has more storage, more processor power to process it (in a DAW etc.) and can convert it (import settings: MP3, AAC etc.) in iTunes (or other apps).
The AAC option provides smaller file sizes, so is more suitable if you need to email, or upload (3G).