you do not need any special baluns IR will happily run over cat5
Easiest way to do it would be to cut the emitter cable in half, the inner cores should be colour coded with red, green & bare cable for the shield/ground, splice these to a cat5 cable also cut in half to the orange, green & green white for ground etc, do this both ends then patch the cat5 to the correct ports, connect the 3.5mm jack plug to your system & connect the emitter to the sky box.
Hopefully if you have done this all correctly then it will work if not you will have to check your connections.
Good luck!
Simon