For sound issues there are two places to start your checks.
First in Windows Control Panel> Sound properties; what is the default audio device (JRiver WDM or something else like Realtek)? And can you get sounds from the device selected when you select it and click on properties >test?
Then in JRiver, Tools>Options>Audio what is the device selected there? The under Audio device settings do you have "bitstreaming" set to "none" or something else?
Lastly, in Audio section under DSP studio >Output Format, do you have anything setup there (under "sample rate" and "channels").
The answers to these questions, I think, will help us figure this out for you.