USB audio out

I have a Pi2B+ with Hifiberry Dac+ running Volumio 2. I was trying to get audio out of the USB to my external DAC so that I can compare the two. Is this possible?

Yes, this should work, although you have to realise that RPi is not always doing a good job with usb. You will have to try it. USB audio should show up in the playback options list.