Recording with Rane MP-2015

I've set up Rekordbox just fine with my Rane MP-2015 mixer, but I can't seem to get the record feature of Rekordbox to work.

In the preferences pane, it doesn't let me select anything for the record input.  

The Rane supports a session out (I use it with Traktor), is there a way to get this working in Rekordbox?