FYI, the "audio only" output on the Oppo is not actually audio only. It's a full audio/video signal but it's raw unprocessed video. The "Audio/Video" output on the Oppo is the video signal that adds all the video processing which you can configure in the Oppo menus (color space, noise reduction, color/hue adjustments, etc.).
The only device that I think might actually separate out the audio stream from HDMI is a Lumagen Radiance video processor. I have not tried this, but Radiance has two outputs and you can configure one for "audio only" and the other for "video only".
You could try that Orei splitter that cleeds suggested. Not all HDMI splitters are equal. If this doesn't work, you might try a Gefen Toolbox splitter (part #
Gefen GTB-HD4K2K-142C-BLK
). They are very expensive, but are engineered better to support different HDMI protocols/devices.
