Chord Co. does an excellent analogue lead (sold in pairs).
Do you have your speakers set up in 7.1?
If you only have a 5.1 setup, connect the leads to correspond with what you have i.e. front left/right & centre, surround left & right and subwoofer.
If you do have a 7.1 setup, you either set up as 5.1 or set up as 6.1 using your surround back left as a 6.1 setup, if this make sense.