You could try a few different driver selections in J. River Media Center.
You should be taking advantage of the ability to use one of the internal Windows Mixer bypassing driver modes rather than the default Direct Sound or Wave Out.
If you're already using one of these preferred drivers, see if one of the other ones might solve the problem. Go to Tools > Options > Audio > Output mode and try WASAPI, WASAPI - Event Style, ASIO or Kernel Streaming.
Steve