This project started with a location that needed headphone audio at a desk. We had an extra cat 5 running to the desk from our audio rack in the other room. So I started out by making these RJ-45 to 1/8 inch headphone jacks.
They worked but the audio was low due to attenuation over the cat 5 cable. I started with a cMoyBB v2.03 headphone amplifier from http://www.jdslabs.com/item.php?fetchitem=cMoyBB203
This project was an easy one and made the client very happy.