How do I connect to secondary on a multi-subnet availability group?

I have multi-subnet in two location ( Boston and Atl)

Boston (Primary):

2 physical servers: 1) BosProdSQL1  2) BosProdSQL2 

Installed  SQL Server as named instance

ATL (Secondary):

2 physical servers: 1) ATLProdSQL1  2) ATLProdSQL2 

Installed  SQL Server as named instance

All 4 servers are in a cluster and Asynchronous mode

I have one AG name Wrk2012AG

Now I am creating a snapshot in ATL (Secondary).

Problem:I can't connect to the secondary instance using say: ATLProdSQL\ProdSQLAG.

I can only connect when I am in any of the four nodes.

I need to run my adhoc and nightly jobs off this snapshot.

Any suggestion please.

Thanks

Datawarehouse lead Architect