Slingbox has a handy little page (
http://www.slingmedia.com/go/help-me-choose) to help you choose which box is right for you. After clicking three times it appears that you would want the SlingBox Pro.
I have the Slingbox AV and it is just to serve up content from one input device. This suits my needs just fine as I have a DirecTV receiver in my office that only I watch. Having said that, think of watching your "slung" media exactly as if you are sitting in front of the TV. Anything you watch or if you change the channel is displayed on the TV as if you were right there running the remote control. So... If your significant other is watching Oprah at the exact time you wish to watch something, you may end up sleeping on the couch if you interrupt the "My Favorite Things" show by changing the channel.