(Don't have iTunes in front of me; there's probably a better way, but this should work)
Look at the bar with the titles of 'artist', 'album', 'title', etc. Right click it, you should get a list with all the details it will display. Choose 'file type' or 'type' (not sure). Play with sizing the window and reducing other items (such as artist) until you can see what you just added if it isn't on screen. Click the type/file type button to sort by that, select all the non-AAC files in blocks using the shift key.
Alternatively, you could probably write a script to do it for you, but you can figure that out yourself, thanks
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