Hello,
when you have setup SSO for your domain users, CIFS and SharePoint will not work for external users at all. You might be able to get WebDAV to work when you point users to the Alfresco Explorer login page first, but WebDAV will also not work for mapping network drives, since you only can access the login page from a browser.
For the interfaces listed it is pretty much impossible to have SSO via Kerberos and access for external users at the same time, unless you support some kind of authentication federation where your AD trusts the AD / DC of the external users (if there is any).
Regards
Axel