Ok, it wasn't easy, but I was able to find the kind of connector the TV has (I don't know all the names, I only know most by sight).
Not all is maybe you should contact LG help line or the manual to make sure I don't say anything stupid.
First, I recommend using the a digital medium for the image (DVI to HDMI cable or DVI to HDMI dongle + HDMI cable), much less quality loss due to the cabling and everything, you should be able to find something fairly cheap online. This one should be plugged in HDMI port 1 of your TV, which is marked for DVI (on the
brochure I found). You should then be able to plug your soundcard's output directly into your TV (just below the VGA connector marked RGB) using a male/male mini stereo jack (2nd connector from the right on
this picture).
Just look behind your TV and tell me if my instructions were clear enough.