I second what Mellow Hudson Mike does. I run a legacy and conventional locos with the same setup. Transformer feeding the Legacy Powermaster that is controlled by the Legacy base and remote. Legacy Powermaster set to conventional. I never use the Legacy Powermaster set to command mode. The powermaster runs both conventional and Legacy/TMCC engines this way.
To run conventional, select the Legacy Powermaster "track" ID and use the remote to run the voltage to run the conventional engines.
To run Legacy/TMCC, select the Powermaster and set track voltage high, then select the legacy/tmcc engine number on the remote. This then runs the Legacy/TMCC engine. No switches. Just remember to set the voltage high for Legacy/TMCC engines.