Soddim, the Nimrod had a full mission simulator and needed several experienced instructors outside to provide the world interface. The Nimrod was easy because a lot of the time it was out of contact but as soon as it got into the close support game the sim staff soon became voice limited.
You cannot play a radio tape as background because that is exactly what it is - noise.
In the Sentry sim we had lots of ASOPs who operated from scripts. Even with 8 or more we were still limited on the amount of RT we could trhow up in the air. The background noise also had to be switchable. If the fighters shot down the bomber then the zippo calls and SAM engagements had to be switched off.
Great fun, cheaper than the real thing but it did need lots of hired help.