The whole point of an AV receiver is to coordinate audio and video signals, so it may not be designed with the capability to deliberately cross up two of those signals. If the AV receiver can't do that natively (search the manual), this problem may be more easily solved with an external switch box.
https
/www.amazon.com/TNP-Switch-Switcher-Selector-Output/dp/B071ZDGVG2
Rig up two of your speakers to the switch output. Send zone 1 and zone 2 to the switch inputs. Leave the radio playing on zone 2.
■When you want to listen to the TV, set the switch to zone 1.
■When you want to listen to the radio, you just turn down the TV volume, and flip the switch to zone 2.
If your speakers need an amp, you can add one between the...