Interesting
device. Short of something like a DVDO Edge, I haven't found anything that breaks out an HDMI signal into separate audio and video signals, and even the Edge breaks it out into separate
HDMI connections. Most likely part of the problem is the variety of signals that HDMI can (in theory) carry: anything from PCM stereo up to multichannel PCM, DSD, and lossless bitstreams. Only about half of the digital audio formats supported by HDMI can be carried over coaxial and optical, so a break-out box that changes to a different digital format could be problematic.
The best bet might be to use the HDMI output for video and the stereo analog output for audio. I couldn't find anything on Netgear's site to indicate what audio formats it supports, but failed. If it supported Dolby Digital bitstreams, using the stereo analog would be a bit less than ideal, but if it's limited to PCM stereo then the analog output isn't such a restriction.