If the DAC is displaying the correct sample rate then JRiver is successfully sending the audio stream to the DAC, so it's mysterious that you're not getting sound. Not to make a dumb suggestion, but I assume that you've checked that nothing is muted (not JRiver, not the alsa mixer, not the physical device via it's own volume control, etc.) and that everything is correctly connected downstream of the DAC (i.e. DAC connected to amp, amp on and connected to speakers, etc.). Sorry for an obvious suggestion, but I've never personally seen a playback problem where the DAC was actually getting signal.