To connect to a Bluetooth device the device has to be set up in the system first.
This will usually be done from the panel Bluetooth applet.
Only after we could sucessfully pair an audio device, and after this device was also availabe as an audio output device in our sound settings we can use stream2ip to auto-connect to this device.
Give in the devices’s MAC or Auto for auto-discovery (in case there is one audio device only).
After a reset to the pulseaudio server we will have to re-pair our device to be recognized.
See also my more Bluetooth oriented project: bt-autoconnect on Launchpad.
Example settings lines: