I found a way to get it to stop being garbled - perhaps my experience can help point JRiver to a solution.
On my PC, this works (or doesnt work) consistently. I have an NVIDIA graphics card. If I use the NVIDIA control panel (after right clicking on an empty screen) to set screen resolution, regardless of what resolution it is, the audio is garbled.
However, if I use set screen resolution in Windows - audio is fine. Go figure - beyond my abilities to comprehend why. ? Just thought I would share.