The AAC option is just to tell HD621 to switch to bypass when it sees AAC. If your 861 doesn't handle it, it won't matter what it's set to. So it's not there for the 861. Why would you ever want any of the format options off with any processor? It should bypass all of them otherwise it corrupts them.

- Fiddler (IMHO)

If you think listening to music is fun, try learning an instrument.
HT: G61RSL, 4x5K, 5.5KHC, 2xSC6000, Transporter, HD621, Philips BDP7501 4K, Tivo, 65" LG OLED 4K C6
Computer: Foobar2000, 5K, Mojo, HiFiMan HE1000 V2