I think given that a power command turns them both on or off I assume the DVD 1600 is one of the earlier Denon models that used the Panasonic protocol and not the Denon(Sharp) protocol. The codes above are for Denon and are the standard discretes for Denon protocol for DVD players. If they are both using the Panasonic protocol I'd think it would be very unlikely to find sepearate codes unless one of the devices can be set to different code set- Tivos for instance can have many different sets so you can use multiple units in the same room. I assume that play and stop are common as well?? if not you could try play stop as an On command for one of the devices.

dwg