Doing a quick google, uSirius seemed to be an app made for the iPhone.
What is it you want to do, stream music from your iPhone, through firefly, to your soundbridge? Not gonna happen.
Stream music from your iPhone to your soundbridge? Only if that uSirius app uses the DAAP protocol and acts as an Itunes share, which I strongly doubt.
I’m afraid I think it’s not possible to use uSirius with Firefly or the SoundBridge.