Looking into this home cinema stuff myself (not via a PC) and it's all changed since my teenage days when I last set set up a system with my trusty NAD 3020 and Linn turntable driving wharfedale lintons (or was it dentons, long time ago).
Anyway, get the feeling that the Sky HD+ will only output the surround sound via an optical cable. That goes into an amp (now called a receiver which I always thought was a radio) which drives the speakers. You aren't going to drive the speakers from the tele.
Also amps (sorry receivers) now cost hundreds of quid, whereas a decent set of budget wharfedale front speakers (diamond 9.1) are less that I paid for my wharfedales 30 years ago. Would have thought with the drop in electronics prices you could get a decent amp for fifty quid now!
So not sure where a PC would fit in....
But as I said, I really don't understand it all now.