Just a follow up in case anyone else has the same question: I got the Roku Ultra which came today, and connected it via the included HDMI cable to the back of the Oppo 103. It works beautifully. Now I've got everything--Amazon, Youtube, Netflix--running through the Oppo, with the audio going through the Oppo's RCA's into my Eastern Electric Minimax pre.
I especially appreciate the Roku Ultra remote's voice command capacity, which allows one to search via voice even on Youtube.