Sorry Rich, you are right ! I made a mistake in interpreting the question !
I disagree; it's absolutely no problem to run multiple instances of Player with their own Stage simulations.
Simple experiment: with player and stage installed, try
[terminal 1]$ player /path/to/simple.cfg
[terminal 2]$ player -p 6666 /path/to/simple.cfg
(simple.cfg is located in the Stage source, in the "worlds" directory)
The seperate instances of Player each create their own instance of Stage. The only limitation is that you can't have more than one instance of Player bound to the same port on the same machine, hence changing the second instance's port to 6666 with the -p switch. If try to fire up a second Player server on the same port, you'll get an error having to do with "Address already in use". Other than that, both Player servers are able to communicate with each other, and clients are able to communicate with each (or both) instances of Player.
If you provide more detail about what you're trying to accomplish, we can give you a better answer.