I see the point you raise about Sonos not wanting to publish this
information. However, I think it is short sighted on their part. They
are currently in a position where they can lead this ecosystem and
define/own the platform. Getting developers onto their platform only
strengthens their position which will result in more of their hardware
being sold. Trying to own this entire market as a single, small company
is an uphill battle that I doubt they can win.
If not, they should help out a bit. You can use Device Spy to control a
ZonePlayer, and then view the exact XML code that was sent (for
implementation in your own programs). I think Microsoft has their own
UPNP DLL which you may prefer.
And of course there's the source code in previous threads in this
forum. Sorry I can't be of more help - to tell the truth I'm more of a
user than a programmer :)
There may be more info in old DE threads too.
I have been using the Intel UPnP tools and still have a great many
contacts there as well as at MSFT from my days working there.