Two places to go: Options/Device Order/Wave In tab: make sure all the inputs show up in the right hand field, and also check and uncheck the "Try As WDM" box to see which one works. When you find out, make sure the same setting is selected for each pair of inputs.
On the left end of the track display in Multitrack View is a little box that says "Out XX" and below "In XX". Left click on the associated buttons and a dialog box will come up listing the inputs you selected at Options/Device Order/Wave In. For example, you can select Track One: 1L; Track Two: 1R; Track Three: 2L; Track Four: 2R, up to however many total inputs you have. These selections will show as as "In 1L" etc in the window after you have selected them. This should allow multitrack recording.