Hi,
This situation is a little tricky, and I am not sure what the correct answer would be, but the Dynamics 365 downgrade paths is as follows:
Dynamics 365 Server corresponds to Dynamics CRM 2016 Server
Dynamics 365 Sales/Customer Service CAL corresponds to CRM 2016 Professional/Basic CAL
Dynamics 365 Team Member CAL corresponds to CRM 2016 Essential CAL
There is a link on the 365 License Guide that points to earlier versions:
Dynamics 2016 Server Corresponds to CRM 2011 Server
Dynamics 2016 Professional CAL Corresponds to CRM 2011 CAL
Dynamics 2016 Basic CAL Corresponds to CRM 2011 Limited CAL
Dynamics 2016 Essential CAL Corresponds to CRM 2011 Essential CAL
Based on the above, I would suggest as follows:
For CRM 2011 Server License, buy Dynamics 365 Server License
For CRM 2011 Professional CAL, buy Dynamics 365 Sales/Customer Service License
For CRM 2011 Basic CAL, buy Dynamics 365 Sales/Customer Service License
For CRM 2011 Essential CAL, buy Dynamics 365 Team Member License
Again, this is subject to license agreement, and the best source for getting the exact licenses and configuration you need might be through Microsoft Licensing.
Your can try Open License and see if that gives you the exact licenses you need.
Hope this helps.