Hi Joris,
look at the NewTek TriCaster XD300. Its a SD-/HD Switcher and has also the possibility for web streaming (also to Livestream,Ustream etc as a built in interface). It can handle 3 HD-SDI Cameras. So theres no need for extra equipment - Studio in a Box. Maybe only a Audio Delay line controller to adjust audio delay (in some cases)
http://www.newtek.com/tricaster-300-home.html