I am pretty certain that you can run a Optical cable from the OPPO (optical output) to the Optical/Toslink input connection on your Onkyo. Dont stress the OPPO has so many ways to connect. Also, you can use a Digital RCA from OPPO to COAX Input on ONKYO and you could use a pair of RCA analogue cables from OPPO to ONKYO. SO you see there are many ways to connect.
Matt
Matt