Whilst this is a photo copy, and some of the pages are a little askew, it was all readable and intact. A real bonus finding an old manual for a classic piece of kit that no other site had.
Text excerpt from page 18 (click to view)
When you have more than one Sony DVD player
If the supplied remote interferes with your other Sony DVD player, set the command mode for this player and the supplied remote to one that differs from the other Sony DVD player. The default command mode setting for this player and the supplied remote is DVD1.
Slide the COMMAND MODE switch on the remote to select the command mode (DVD 1, DVD 2, or DVD 3) so that the setting for the remote differs from the other DVD players.
For example, if other DVD players respond to the default command mode setting for the supplied remote (DVD 1), set the remote to DVD 2 or DVD 3.
Slide the COMMAND MODE switch on the rear of the player so it matches that of the supplied remote.