@thomas204 I haven't tested case sensitivity, but I have got a lot of "internal server errors" too, while trying to get the commands working, so I have have just followed the examples I have come across literally. Also, in my setup the contents of the body field is one long string.
Then following example selects a specific radio stream (the rest of the fields are identical to those in my previous post):
Body: <s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/" s:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/"><s:Body><u:SetAVTransportURI xmlns:u="urn:schemas-upnp-org:service:AVTransport:1"><InstanceID>0</InstanceID><CurrentURI>x-rincon-mp3radio://live-icy.gss.dr.dk/A/A03H.mp3.m3u</CurrentURI><CurrentURIMetaData /></u:SetAVTransportURI></s:Body></s:Envelope>
-Dennis