Hi Mark
Concerning the B2 and Sonos, it will work with both S1 and S2 but any reason not to use it with the Connect Amp, as that system is already working? The B2 has a Line Out (variable level) or an optical (digital) out (fixed level) - may require an external DAC if the Connect doesn't have an optical in - which can be used to feed the Connect Amp.
As far as I know the B2 will attempt to import all files on the external drive but you can use the USB menu, via the web UI, to download selected files. If the HDD has a 'hardfi' folder i.e. a JB7 backup, then select that to download.
Paul
Brennan Support.