Since you cannot rearrange your room surround sound would not work well for the different seating locations that you have so I would go 2.1 channel with 2 pairs of speakers. One pair at the PC when you are at the desk and another pair for the TV when you sit in the couch. A single sub would work for both pairs and you would turn off the pair that you did not want to use. A stereo or surround sound receiver with speaker A-B switch and sub out would work. You would feed it with the audio from you PC and your TV (or set top box if you have one). A surround receiver might be easier to connect as it will have digital inputs. You can divide your budget as to which pair of speakers is more important.