In the Toshiba system, that is true that if a supervisor is logged into the Toshiba ACD system and has selected to take calls, that they will only get calls if all the other ACD agents are not available.

You could just have the supervisor log into the system as a regular ACD agent if they don't need the supervisor functions. Logging in by phone would be easy. You could give them an ACD agent login number when they need to be supervisor and a different ACD login when they need to be a regular ACD agent. You will need 1 additional ACD agent license. While I normally associate an ACD number with the user's extension number, they do not have to match.