are u talking about a 5.1/2.1 (such as creative inspire) for PC to be connected to TV or a dedicated 5.1HT ??
i assume u r talking for the PC 5.1.. then it depends on what input ur speakers can take.
I do not have much idea on how to find a compatible connector but I have a creative inspire 5.1 which i can not connect to my LED tv directly coz it has 3 input jacks. perhaps there is 3.5 x3 female connector converter or something
But my iball booster 5.1 had the possibility to connect 2.1ch via 2xRCA->3.5mm. but u get only 2.1ch. Else i had to connect it to my DVD player which receives 5.1ch connection and input from tv. but gotta keep all 3 units running!
if your 5.1 unit has a provision for 3.5mm mic in, then get a 3.5mm-3.5mm cable and it should do..
but i suppose basically the tv out is just 2ch :-/
there is an option (well.. its there on my samsung led) to select external speaker which mutes internal speakers
Hope the above solution works for u
PS: Anyways i realized all the above was too painful and definitely not better than my inbuilt speakers, i invested on a Yamaha AV receiver with 5.1. Advantage with an A/V unit is you can always connect most speaker systems