Well, i own a soundtouch device and am happy with its sound quality. But the the actual component does not play media from https:// urls only from http://.
But the soundtouch boxes are capable to play these urls by the notification api. You only need an appkey from the bose developer program. With the appkey, you can get one free for 100 calls a day, it is easy. Just post an XML string and you are done.
val String PostData = '<play_info><app_key>' + AppKey + '</app_key><url>' + TTSUrl + '</url><service>OpenHAB</service><volume>' + Volume +'</volume></play_info>';
sendHttpPostRequest("http://192.168.178.xx:8090/speaker","",PostData)
Perhaps it is possible to add an appkey value to the configuration data and if it is present use the notification api to play the url instead of using the libsoundtouch play_url method.