OK, I discovered the problem.
When I was working through the 3rd party certificate issue, I had changed the bindings on the default Website from "All Unassigned" to the specific IP address of the server. Changing it back to "All Unassigned" resolved the issue and now I can launch EMC and EMS and connect to the gs.mail.gs.local server just fine.
I will give some points to Burns2007 since he suggested that I uninstall the gs-test Exchange server, which didn't really solve the problem but doing so is good practice as it turns out.
Dave