It does not support AAC. The DACs in the main pod/sub are 16bit/48KHz, but pretty nice quality. You can send 24bit/96KHz and 24/192 streams, but they are automatically downsampled at the DACs.
I've gotten to know my Z-680s pretty well. Best money I've ever spent on computer-centric A/V gear.
It handles AC3 and DTS over digital links, but not the WMA-Pro 5.1 nonsense, and not AAC.
It can decode MP3 sent over the digital link, but it's not designed to do it, and there's not much point.
pa' ngaSwI' nuq vay' Data'nISbogh roD tu'lu' tlhIH'a'?! yIn jaj tera' na'ran wIb laH HInob Qub 'oH rue munISbogh 'Iv ghaH DaSov'a'? loD chay'pen tuqwIj meQ 'Iv jIH! TERA' NA'RAN WIB! chay'pen burns tuq vI'ogh 'ogh, chombuStIble tera' na'ran wIb!