The only direct way would be via an Oppo mod'ed for AES outputs, which are long since unavailable (there are some modders still offering these features, I see, but not cheap, and who knows how reliable?)
I eventually gave up on that and just bought a USB ADC (Motu 8Pre USB) that takes the 8 analog outputs and feeds them via USB to my source PC, and from there (via JRIver, in my case) out to the OktoDAC via USB.
Not elegant, but it works, gets me the Mch decoding I wanted for Blurays and streamed content, and doesn't cost an arm and leg!
Or, just bite the bullet and spring for an Oppo 205 ($$$$) and switch outputs between that and the Okto for Mch movies..performance of both is pretty much the same.
What is the point of doing DAC -> ADC -> DAC ?
You are applying a transformation in the middle like EQ or room correction ?