The B2 does not send audio over any network, neither wired nor wireless. Sonos speakers are a special case, for which special programming has been done.
Sonos speakers, of which there is much discussion, use the B2 as a network storage device and pull audio *files* from the B2's hard disk. The B2 is not "playing" the files and sending the music: the Sonos speakers do all that on their own.
If you connect your passive speakers to some intelligent device that can use a networked drive and get the files, then play them through those speakers, that can be made to work. But the B2 won't know about those speakers, it will just be a networked drive for the other device.