I don't want to kill the enthusiasm, but I suspect it's a typo. They are referring to various Surround Sound formats this receiver can process for home theatre. I think they mean MPEG 2 AC3, not AAC.
Dolby digital EX, the DTS-ES and Dolby professional logic II, in addition to the DTS NEO:6 and the MPEG-2 AAC et cetera, it corresponds to also the DTS 96/24 which is the up-to-date format.
Edit: Anyway, AAC is dead (or so says Neo Neko). If it isn't dead yet it'll die soon. So, no reasons to commemorate, really. :B
Now someone is going to come in here with a 500 word post arguing about AAC, and then follow up with another 500 word post saying that he isn't the one arguing!
"Sony knows what's good ™"