Direct vs proxied MP3 streaming

I am trying to use direct MP3 streaming for Classic FM to my Duet Receiver. This is intended as a work around for router issues, my router has a limited NAT sessions pool per IP and if it can see MP3 streams as going to the Duet that will give them their own pool (and thus should not run out). But even with "MP3 Streaming Method" set to "Direct Streaming" I am not seeing the Receiver's IP address in the NAT sessions table display on the router when playing Classic FM. The router shows plenty of NAT sessions for my server, and some for my iPad and my laptop, so I think the router's NAT sessions display is working.

LMS 7.8.0 on WHS v1. What server logging can I turn up to find out what is going on with the MP3 proxied vs. direct playing?

I am aware that if sync'd play is in use all streams are proxied. I only have one player on my network.