| That is a bunch of questions!
1) There are 2.4 GHz wireless speakers on the market. Just remember they each require a power outlet, thus making them not really wireless.
2) If your talking about a Home Theatre in a Box (HTIB), a bundled amp with speakers vs. buying each part seperate, here is my opinion. I nice $500+ HTIB form Onkyo or comparable would probably suffice for the majority of home theater gamers out there. Can you listen to MP3's without complaing about the poor audio quality? If mp's sound fine, I doubt you have the "ear" required to notice a difference from a $500 setup to a $5000 setup.
3) Most amps have 2-4 optical audio inputs. If your devices are using HDMI, a newer receiver can take the single hdmi cable and get BOTH the audio and video into itself. And then pass the video back to your tv. This is the best way to go.
4) Most receivers have methods of controlling which speakers are on. I am not sure I have seen one that allows a 5.1 to use only rear speakers in stereo mode though. It might be possibile, but it would be goofy. Almost all amps do have speakers set A and speaker set B. A is normally the 5.1/7.1 output, and B is normally a stereo option. This makes it very easy to do what I think your trying.
Good luck! | 
