I've just finished connecting my B2 by ethernet for the first time. The wifi was fine, but I've got the current problem with BT broadband, as described in another thread, so couldn't use the web UI as my B2 is on one frequency band and my tablet on another.
I bought a short ethernet extension, as recommended here, to hang out of the back of the B2 and ran a cable from the router to meet it. Fitting the extension was easy, though I had to be quite firm in bending the cable back on itself to take it out of the (round cable)slot on the rear panel. There isn't much room in there.
I also fitted a replacement SD card I've had for a while, so now have B2B software rather than the old B2 version. Now updated to the latest issue. It's recognised our various Sonos speakers around the house.
Everything seems to be working on ethernet. The IP address changed, as I'd expect, but I can now access the web UI again, even if BT fail to come up with a fix for their broadband issue.
I even remembered to remove the B2 wifi dongle, as I think I've read it can cause problems when it's in there alongside an ethernet connection.