your HT only has two inputs...
r+w rca (you could use a 3.5mm stereo male to 2x rca connector) that will give you 2.0 sound only
or you could use optical out of your motherboard (if you have it). though i'm not sure of 2 things. 1) if your motherboard supports DDL (needed for 5.1 over optical) and 2) if your HT even allows more than stereo sound from an input (which often is not the case in cheap systems).