The ping-pong recording process is as follows:
1. In the Patch IN screen (AW4416: [SETUP] + [F1], AW2816: [PATCH] + [F1]), set the "Recorder Track Input Assign" of each track to bus 1 -- 8.
2. In the Pan MONI screen ([PAN] + [F3]), assign the tracks (channels) you want to record to the same bus.
3. Adjust the mix levels and record to an empty track via the bus you assigned in the previous step.