Does anyone have any experience with device codes for Sony CD changers?

I have two Sony CDP-CX300 CD changers. On my old Sony receiver remote, I could program the CD function to control one player and the AUX function to control another. Code 001 controlled command mode 1 and 003 controlled command mode 3 (the Sony changers have switches on the back of the unit and on the remotes to set the command mode).

The only control code in the manual that works on my new URC remote is 0000, but that only controls the first player.

For now, I set AUX to a different code (that doesn't work), and I programmed the AUX function to learn the essential commands from the old Sony remote. This works OK, but it'd be nice it there were different codes for the different command modes, so I could free up some memory on the remote that I'm using for learning the commands for the 2nd player.

Thanks in advance for any help!
--Nathan