Don't you mean the A24? The A6 is COM TX/RX only , it lacks the VOR capability of the A24 , so how would FM immunity be a problem?
I mean the French say FM immunity is a problem on the A6. They added the FM filter, called it A6FR and got DGAC approval. Make of that what you will.
Filtre antenne réjecteur bande FM des portatifs IC-A6FR et IC-A24FR pour l'installation à bord d'aéronefs (ne peut être vendu séparement)