Hi Dan,
Thanks for the link. I checked the thread as well as did some additional research, there is indeed a security token problem with mapped drivers, enabling SSO could be a workaround.
In your situation, DirSync with Password Sync could not be a workaround. When using a mapped drive, once the token expires it does not prompt for a login, in this way, DirySync with Password Sync would not able to authenticate users. In other words, you still need to enable SSO.
With the security token problem, we normally do not recommend you use mapped drivers with SharePoint Online, instead, we recommend you use SkyDriver Pro client. It would work just like a mapped driver, you can download and test it with the following link:
http://www.microsoft.com/en-us/download/details.aspx?id=39050
Best Regards,
Evan Zhang