I have not tried BigTalker yet, but using the Sonos code, I have setup notifications for people coming and going. Used Events to Trigger Alerts, and Custom Messages (which appears to create a instant TTS mp3 routed from amazon servers, played on your device). Have not cared to try any music streams yet.
When looking at your DLNA device, the lower PLAY button activates a internet radio station. It is easy to confuse that with the above PLAY button.
On my Fiance's iPhone, i installed the program ULE recommended "Browse UPnP" for iOS on the App Store and it showed many of the devices around my house that were DLNA. You then click on the item and it states the schemas. You need to look for "urn:schemas-upnp-org:device:MediaRenderer:1"
I did not have any luck with various Free iOS apps for sending custom notifications to iPhone or iPad yet.
After some searching, and testing, i can recommend a similar app for Android, its called "UPnP Tool" on the Google Play Store.
That will allow you to verify if your device states MediaRenderer:1.
Glad to hear it's working on the Squeezebox. Id love to buy some cheap $40 Android tablets and mount them in various rooms however none seem to have very good speakers.
Hopefully I can make some time this weekend to play some more, you guys are making me jealous!