I'm not sure what you mean by playback to ethernet.
You can control the B2 from the WebUI, which requires that the B2 be connected to your home network either by WiFi or direct ethernet cable.
You can access the B2's HDD when it is set up as a NAS drive, and that can also be accessed when the B2 is connected to your home network either by WiFi or direct ethernet cable.
However, you cannot run the B2 with it connected directly to your equipment by ethernet cable. It must be on your local network.