I’d like to add this information in case it helps someone in the same situation I was, because a lot of people are trying to use non-original AV or stereo leads with their TV Live and not getting good results (I was one of them). I was looking for exactly the kind of solution that I am posting now, because my TV Live only came with the AV Out cable which I had lost and not the composite cable which can be a solution to people who have that cable.
Sometimes when you hit a problem you just have to find a solution *that night* 
So… I wanted to attach the WD TV LIve to a pair of USB powered 2.0 speakers. I had lost my original AV Out cable and the other AV cables I had did not work with the unit, resulting in a loud buzz or no sound from one channel. Eventually I managed to dig up a Nokia AV Out lead from my old N97 Mini, an RCA-to-3.5mm stereo plug lead and two female/female RCA couplers. (You can drop the RCA-3.5mm plug cable and couplers if you are trying to attach the TV Live straight to an amplifier with RCA inputs… if the Nokia lead is long enough to reach the amp!).
The Nokia AV lead is plugged into the back of the TV Live and has red, white and yellow RCA plugs. The RCA-3.5mm lead has red and black RCA plugs. I connected the red plug of the RCA-3.5mm lead to the red plug of the Nokia lead (via an RCA coupler) and the black plug to the YELLOW plug of the Nokia lead… because I got another loud buzz if I tried to connect the black plug to the white plug of the Nokia lead.
For an amplifier, red to red and yellow to the other socket should also work (but I take no responsibilty for personal injury/flash fires or loss of home/worldly posessions). As far as I can tell I’m getting clean stereo sound
