finding the remote IP address used by a mounted SMB share
Since it is advertising its presence on the network with Bonjour, you should be able to simply ping it:
ping -c 1 nas-smb.local
I had problem of finding IP of maching which is not even behind NAT. Finder shows the name Bonjour Exporer and ping does not resolve it. Finally smbutil lookup <name> worked for me.