I have a Sony 850D (200-disks), 860D (300-disks), and a Pioneer F727 (300) disk that I control with my Pronto.
I have not found any discrete codes but there are specific sequences that allow you to select a particular slot.

I would be happy to share my CCF if you are interested. I have an indexed alphabetical list of all of my DVDs that allows me to select any movie by name.

Otherwise, the sequence that I use is ON, STOP, WAIT=7sec, STOP, WAIT=0.5, STOP, DISPLAY, DISPLAY, CUR-RIGHT, #, #. #, ENTER, DISPLAY, DISPLAY. Where #, #, # is the disk number (you don’t need to enter leading zeros). I actually put WAIT=0.2 between each code just to be safe.

This seems to work regardless of what state the player is in (on, off, playing, paused, setup, …).
This sequence works for both the 850D and the 860D. There is a different sequence for the F727.

I like the Sony much better than the Pioneer, I just wish that I could daisy-chain them like Pioneer allows.

Bill…