The first prototype is now working for the IR Repeater. I'm using the IR Extender Mark 4 circuit powered by a 9V battery. There is an extra fat wire connected to the circuit that isn't currently used; it is a USB cable that I'm hoping to use to power this rather than a 9V. My next step is to build a copy of this on another breadboard and modify it to use only 5V instead of the 9 / 12V most other people use.
Above is the prototype in the cabinet in use. I'll make it more subtle once I get it powered the way I want. I intend to run the IR LED under the mat and have the breadboard closer to the hole in the rear of the cabinet. You can see a blue wire going thru the rear of the cabinet and break into 2 to connect to the breadboard. One of the bundles from the blue wire goes to the IR Receiver and the other connects to a red LED that can be used for trouble-shooting. The blue wire is terminated in the wall via a CAT 5 connector.
Above is the panel behind the cabinet. The wires there run to a panel behind the TV. Behind the TV is another CAT 5 cable with the IR Receiver and indicator LED on. You can see it hanging down below the sound bar in the picture below. Once I'm happy with everything, I'll put the LED in the wall and the IR Receiver on the bottom of the sound bar so none of it will be noticeable.
To make sure that the wiring and connectors were going to work out I build this tester. It is very similar to the one I used in my initial sensor bar and IR Repeater tests but I'm using all of the wires needed for the IR Receiver and indicator LED here. I plugged in the powered side by the cabinet and the LED side behind the TV. The lights came on so I was happy. Note that there are reminants of a different circuit on this breadboard. All that was required for this test was the 9V battery and resistor.