Hi KR4. Didn't see your response until now. If I could set to send as 5.1, I'd try it. But when you enable the "Output Format" option that allows you to select 4xDSD output format, it does NOT allow you to choose any channel arrangement except Stereo. Stereo is pre-selected, and grayed out so that you can't change it.
It would be ideal to be able to select whatever channel arrangement you want as output, and then have JRiver convert to that channel arrangement while still in the PCM domain (using JRSS mixing if required), and then convert from PCM to 4XDSD in that channel arrangement for output, be it stereo, quad, 5.1, or whatever. I'm sure most modern multi-core CPUs have the horsepower needed. When I play a quad 192k file, converting to 4xDSD stereo (since that's the only option), JRiver runs at about 5% of CPU, so it's obviousl that there's plenty more horsepower to convert additional channels. We just need JRiver to allow that option.