Hugh,
Daniel is correct. The B2 can act as a NAS. You can enable this on your B2 by going into the B2's menu options as shown below (this is using the latest software release dated 09th Jan 2020)
On the B2 go into 'Menu' - 'Settings' - 'Maintenance' - 'Start NAS'.
This starts up NAS on the B2.
Then, on your PC, assuming you are using Windows 10, check that 'SMB1.0' is enabled. You do this by going into:
'Start '- 'Control Panel' - 'Programs and Features' - 'Turn Programs and features on or off' (top left on the screen) - Scroll down to 'SMB1.0/CIFS File Sharing Support'
Click on the '+' on this option to open it up, and check that 'SMB1.0/CIFS Client' and 'SMB1.0/CIFS Server' boxes are ticked. If not, click on each of these to enable them. Click 'OK' to confirm the selection.
Close down all of these windows.
After a few minutes, if you open up Windows Explorer, under the 'Network' section you should see an icon called 'BrennanB2'. If you click on this, you should see a folder called 'Music'. If you click on the 'Music' folder you should then see all of your music listed.
You can then manipulate these files and folders as you require from your PC, as if the files were on your computer.
It's a great way of managing your music files on the B2.
As Daniel says, you don't need a separate NAS drive at all. However, you should back up your B2 music to your PC or other storage area as a matter of course. In Windows Explorer, I created a 'BrennanB2' folder on my PC, then dragged the B2 'Music' folder over to the PC 'BrennanB2' folder. It took a few hours to complete, but it was worth it to know that I could, if necessary, rebuild the B2 from scratch without having to re-rip all my collection.
I bought a Brennan BB1 in September and built it by enabling NAS on the BB1 and just dragged the B2 'Music' file onto the BB1 in Explorer. A few hours later my BB1 had all of my B2 music. All done in one 'drag and drop' click operation. Superb!!
Regarding your other query, I looked up the B2 back panel diagram on the Brennan site and the micro-USB is shown as 'Not in use'. I didn't realise that there is a micro-USB slot! My B2 is an older model (about 3 years old now) and doesn't have this.
Like you, I love both the B2 and BB1, and have had many many hours of pleasure from them, and I wish the same for you.
Regards,
Peter.