SQL Server transactional replication distributor If I have a SQL Server 2012, with two databases, both publishers, replicating to a bunch of subscribers.  


Can each database go through a different distributor?
Is the publisher the server or the database?  


I understood it to be a publisher can only go to one distributor


Is that each db or the whole server?
The Distributor is the server that contains the distribution database. 

Configure Distribution at https://msdn.microsoft.com/en-us/library/ms151860.aspx says: 


  By default, the Distributor is the same server as the Publisher (a
  local Distributor), but it can also be a separate server from the
  Publisher (a remote Distributor).


SQL Server can support a single Distributor on the local server.  If you are trying to reduce the load on the main server you can instead create the Distributor on a remote server.

If the load is heavy, an additional step that would help manage the distribution is to create a distribution database for each database that is being published.  This could reduce the contention within each database that might be present in a single distribution database.

Both a local server and a remote server can support multiple distribution databases.

David Poole's article from 2010, Scaling Out the Distribution Database. may provide you more insight.  It can be found here: http://www.sqlservercentral.com/articles/Replication/69663/ 

Both articles are helpful and I have not detailed every step in the setup.