the only way i can see you doing this with a p1 is to use your left input for a mono board feed and your right for a mono mic mix...then import the individual channels into a DAW to mix appropriately. The deck will not mix for you (at least I've never heard or read anything that says it does). If I'm wrong here, someone please correct me, but I highly doubt the dap1 will mix the inputs of mic in and line in for you...
h