You can test the quality using the headphone or the line out jacks into your mixer, and/or powered PA.
I suspect the easiest way is to just use the internal file in native format, by finding the partition the song is in, locating the song, and loading it. You would simply play it, with the output going to the headphone jack or line outs, into your mixer.
If you export the song to your PC first (after mixing it down, and mastering it), you will have a .WAV file. Those can be loaded back into the DP-008, into a selected partition. Then you would load the song, hit play, and again, the output goes to the headphone jack.
An other way is to output the .WAV file on your PC through it's headphone or speaker jack; or to transfer the .WAV file to a media that can be read directly by your mixer or PA, using whatever type connectors they use.
My thoughts on performance would be to have a "Performance" partition on the DP-008's SD card (you can get 32GB cards on ebay for $3-4), just for the songs you'll perform. Use the other partition(s) for creation, mixdown and mastering.
\
Happy Trails...Good Hunting!