Ok, great, one thing cleared up..the Audio Devices tab pertains only to MPD.
Ok, I shut down all devices,then started up the (connected) DACs, then the BDP-2. Pulled up tracks from via network and still no USB output.
What step am I missing?
In detail you should take these steps
Turn the BDP off
plug the USB dac into the BDP
Power the USB dac on (if not already on)
Select the USB input on the USB dac
Power on the BDP
Wait until the BDP displays the message "MPD Ready"
Turn on the dlna renderer on, restart if already on
If it's still not working which USB dac are you using?