Greetings - and Happy New Year to one and all!!!

I'm about to pull the trigger on the PreSonus HP4 4-Channel Compact Headphone Amplifier and I have a question about how I should hook it up to my Focusrite 8i6 interface.

I've seen some people suggest that I just plug one end of the wire to the headphone input on the front of the Focusrite and plug the other end into the PreSonus. But if that's the way to do it, what are the input/outputs on the back of the PreSonus for? I'm thinking - and I might be wrong (it wouldn't be the first time) - that the connections should be done with these. And if so, how exactly should I be running the wires for this type of connection?

All input (no pun intended) would be greatly appreciated!!!