Thanks for your input Sue.
Memory for thread stacks, memory heaps, non-SQL Server linked server providers and other non-SQL Server dlls are not part of the max server memory.
How can I see more information about these memory users?
When you talk about "non-SQL Server dlls" I think about CLRs which have their own memory clerk. Although we do have some linked servers, they are only used for occasional administrative tasks.
Things such as third party products, user defined extended stored procedures can also use DLLs, it's not just CLRs.
You can find several different things to check the memory usage in this post:
SQL Server 2012 memory consumption outside the buffer pool
Sue