The issue is not the Pronto, the issue is Sonos. To write what is neeeded on the Pronto requires detailed knowledge about how the Sonos operates from a communications standpoint. Please do not tell me they follow uPNP protocol; that like saying the use HDMI. Specifications and protocols are all subject to interpretations and version releases.

When I build an interface to a component be it Squeezebox server, Vudu, Sony changers, etc. I first read all I can about the interface. That itself is often monumentally frustrating. I then write the code (trial 1) and use something like wireshark or etherdetect to capture what is going on.

While "TCP/IP" is a guarnteed delivery protocol, (I will argue that when wifi is in the loop) anything over UDP is "Best effort", so an awful lot will depend on network traffic. As an example when I send out a "Magic Packet" to do WOL I send it about 20-40 times knowing that once the device I am addresing begins to wake up it will ignore all further magic packets.