Can I listen an Audiopoint 3.0 channel with a Barix Exstreamer ?

Yes, that´s possible with the Streaming Client firmware and even with the RTP-STL firmware.
On the Streaming Client firmware you have to configure in the URL :

brtp://IP address of the Audiopoint 3.0 device:subscription port of the channel

e.g.:

brtp://192.168.1.25:9444

To optimize the audio with Audiopoint firmware 1.9.6 it is recommend to use only one channel on the Audiopoint 3.0 setup
and to delete the second channel, otherwise the Exstreamer might have a minor audio issue in the first second of the stream start.

That will even work over Internet when the local subscription port is forwarded on the router.