You have given your server the name dabrain.homeserver.com? Then you need to make sure that you are the owner of the domain homeserver.com publicly on the Internet to be able to use DNS names...and that the www pointer is directing traffic towards your public IP on your router.
If you are not the owner of homeserver.com and that name is only used internally on your local network you have to connect with http://xxx.xxx.xxx.xxx:4365, where xxx.xxx.xxx.xxx is your public IP on your internet connection.
Hope this will help you in the right direction.
He doesn't need to own homeserver.com, just being able to configure dabrain.homeserver.com is enough.
Learning new things every day
Didn't know about that feeature for Homeserver - quite nice.
Anyway I am also able to connect to you WebMP from your external source using http://dabrain.homeserver.com:4365 and IE9.