from what i can guess, you can select from:
2. spdif (coax or toslink)
3. OFF (but USB still works)
... the headphone will always output sound no matter which mode you choose.
for my usage:
i use the toslink audio in. speakers plugged into the "MAIN" output in the back. headphones plugged in integrated jack.
i set the unit onto MAIN mode, and use optical spdif. sound comes out from both speakers AND headphones at the...