Had to do some monkeying to get Stereo Mix to work (works fine on the third set of drivers I tried

so that's all sorted. I've setup Blizzcon 1 and Blizzcon 2 channels for tonight - both are globally muted, I'll un-mute the clients doing the streaming once it gets started.
As Daff suggested it makes sense for people to add a phantom to the Blizzcon channel they want to listen to and just chat in the lobby so it doesn't interrupt the streaming for anyone. To do this right click the channel>miscellaneous>add/remove phantom. I've bumped the license to the server for 25 connections for this weekend, will drop it back down afterwards (the hosts are happy to do a pro-rating of the fees and a couple of days won't break the bank.)
I'll stream the Development stage in Blizzcon 2, if Daff could do the main stage in 1 that'd be awesome.