Use firewall to block ALL Siri connections

[Jonathan_Pitts]

How about creating an allow rule for apple.com in your firewall with logging enabled.
Then watch what hosts it accesses when using siri.

Then create new rules to block those hosts.

You could also enable url logging, see here:

Configuring URL Logging

As of Firmware 6.3, Peplink devices are capable logging the URLs visited by each user. To enable this feature, navigate to Network > Firewall > Content Blocking. Scroll all the way down to see the following menu:Click enable, and the enter the ip address and port (if applicable) where your remote syslog server is located.