Thanks for your response Matt. I'd be happy with that if it worked on my system, but unfortunately the system will wake up and stay awake. I've done some more digging since your reply. As far as I can tell it is J River waking it up, but it is my sound drivers (Sound Blaster Z SPDIF-In) that keeps the system awake (based on powercfg.exe /requests and playing around disabling recording interfaces). I can't override the 'requests' that are keeping the machine awake for some reason (using powercfg.exe /requestsoverride). This appears to be a known Windows 10 bug.
I'm not holding my breath for Sound Blaster or Microsoft providing a fix for either of these issues, so the easiest option may be a tick box in J River's options that prevents J River from waking the computer up. If it's the EPG wanting to update then I'm more than happy for the system to do that when it is on and not waking it up to do so.
I appreciate this isn't strictly an issue with J River. You can add this to the list of feature requests for release 23 if you like! Thanks again.