Using 2 Presonus Audiobox 1818VSL's in Logic Pro

I have 2 separate audio interfaces, but they are both the same, Presonus Audiobox 1818VSL. Logic will tell me when I plug each in that a new input/output is available (2 total now), but can't differentiate between the two. I can only select the first interface that I plug in to use with Logic. I know it's possible on a Mac, but I just don't know how. PLEASE help.