I prefer Foobar 2k over JRivere for Sound quality, but JRiver is a good player, for sure. I would disable all dsp functions, volume leveling, etc for purist bit perfect sound.
My tests with Mojo are that it sounds best running on battery with no usb hooked up to the charge port. And a 1 amp charger may cause an issue that I discovered with the Mojo when it hits trickle charge mode in my speaker setup.
My speaker amp is also on and in a configuration with a passive pre and the mojo in charge mode with only the charge usb cable from the computer, a noise developed in both channels similar to what folks in the Mojo thread describe as hissing. Only there they seem to be talking about ambient hissing from the Mojo itself when using some under powered chargers. I can post the video of the noise if interested.