Try starting the air application as see what happens no need to start streaming music... There is a lot of packet beteween the amp and client. The broadcast packets from the devialet is nothing compare to this. But it is only small packets. I guess that instead of using mulicast they are using broadcast to let clients know it's whereabouts.
Naim nac-n 272, Naim nap-300, PMC Fact 12, Audience AU24SE power cables, Oppo BDP-103D