I'm a new member here and have really enjoyed reading this thread, as I just bought this same TV. I haven't played with the picture yet but regarding sound output, some things I found that may be of use:
The mini jack on the back labeled Ex-link is designed for control signals. It doesn't look as if it can be programmed for any other use. It doesn't output any audio signal.
There is no other sound output, but if you remove the back panel, the printed circuit board (at the antenna connection) has a flat 4 pin connector (that plugs into a socket on the board) that runs wires to the speakers. It's easy to recognize, it has green and yellow wires separated into two pairs, one pair going down to the left and the other to the right. You can test if it's the right one by unplugging then reconnecting while the sound is on.
I used another 4pin connector ( that I *just* got from a 10 year old 55" Mitsubishi that died - lol ) and it plugged right in. The wires easily drop down under the cover when you reattach it. I intend to run these wires to my audio receiver or may run these straight to a subwoofer/satellite speaker setup.
Since I was able to use the connector from the older TV, I believe this is a standard connector that can be purchased.
The benefit of this setup is the TV can be easily returned to its original setup if you need to.
I am also doing some casual visual testing of this set alongside a Sony KDL60R550A for a few days, if anyone is interested