Neither.
Never seen USB monitors before but what a great idea.
Simply go into your DAW and set your preferences to "Line Out, M1Active 320 USB". Something like that. It will offer you the choice.
You can also hook them up to your computer line out. So a stereo jack pin which splits to a L & R RCA "Y".
If you are going to go from the Presonus to the speakers using the 1/4" jacks then go balanced but I doubt that it matters very much.