Big question is: does your TV properly pass-through encoded bitstreams? That is, if any of the HDMI sources is sending a DD5.1 or DTS stream, does your TV pass it on via optical? Does the Sony display 'PCM' or either Dolby or dts logo in upper right corner? If you get proper surround, and are fine with the sound from the Sony, you can just get a Blu-Ray player, connect it via HDMI to the TV, and be done.
If you TV does not pass streams, you are not getting proper surround out of your sources. The less expensive - but less convenient - solution is to get an optical audio switch, and use it to get audio direct from your sources to the Sony. The more expensive solution is getting an HT system that has enough HDMI inputs. Most HTIBs that come integrated wit ha Blu-Ray offer only 2 HDMI inputs. You need 3, maybe more if you sometimes want to connect anything else.