The DR-60D is a 4-channel recorder so there shouldn't be any issue at all doing that. In the menu just set the deck so that all four channels are active. 1 and 2 have their own gain pots to adjust them individually, and 3&4 are treated as a stereo pair so there is a single pot to adjust their levels together. It's all in the manual. If need be, you can adjust 3&4 separately on the MP-2.