RTFM.
From pg 6,
"Connect incoming signals to these electronically balanced Combination connectors, using either XLR or 1/4" TRS (Tip/Ring/Sleeve) plugs, wired as follows: Pin 2 (or Tip) hot, Pin 3 (or Ring) cold, and Pin 1 (or Sleeve) ground. We recommend the use of balanced three-conductor cabling wherever possible (unbalanced two-conductor 1/4" plugs can also be inserted into these inputs, but you’ll get better signal quality and less outside noise and hum if you use balanced lines)."