Most movies are 2.0(stereo) but if you have an home cinema Amp you can connect it to your box and set the sound to passthough...it will go to your Amp passing through your box. There are some 5.1 channel movies on NaviX and Phoenix, when you watch them it will have 5.1 on the pop up menu.
Rooted means you can change things on your box, like adding Apps and even upgrade the system. On an iPhone its like Jailbreaking it.
There a lot to learn on xbmc and it good to have a look round, but as long as it works and movies and sounds fine leave alone. There's a lot of videos on YouTube you can check out too, about most of the setting and how to get the best out if your box. Hope this helps you...
Dave