I don’t think Sonos uses an account/password combo, except when using the controller to access the data, but then again I’m not sure either. I do know it uses SMB v1, but as I recall when setting it up in the controller, there was no account. But it’s been a long time since I’ve messed with that, you could easily just try removing and re-adding the share back in to controller, and see if it does ask for an account. That would confirm whether or not it does ask for an account/ password at that point. 

Yes, you do need to give it an account and password when adding the Share.

You should definitely disable the Guest account too.

Create a new account for Sonos on the NAS with a secure password and just give it Read only access to the Share you have your music on and nowhere else.

Then use those details when adding the Share into Sonos.

e.g. \\diskstation\media\music

Thanks for the replies. I reconfiguring SONOS to use SONOS NAS account with a password.