Looks like you can use the Oppo's volume controlled output to connect directly to an amp.
From the Oppo site:
"Sonica DAC provides both XLR balanced and RCA single-ended outputs, and the outputs can be set to volume-controlled or bypass, making it suitable for connecting to either pre-amps or power amplifiers."
From the Oppo site:
"Sonica DAC provides both XLR balanced and RCA single-ended outputs, and the outputs can be set to volume-controlled or bypass, making it suitable for connecting to either pre-amps or power amplifiers."