For the 360 Have you considered getting the VGA cable? You get a stereo rca phone female jack to male 3.5mm headphone adaptor with it (see below), you would then have to buy a female female 3.5mm adaptor or extension for your headphones.
Your TV should have a vga in, and imo, it displays the best picture for the 360. The VGA cable also has an optical port if you want to use that later. (although i think the component cable also has one). Having said that i think you could do something similar with the component cable.
EDIT
vga cable
or
component cable
This is the thing you get with the official 360 vga cable;
http://www.maplin.co.uk/Module.aspx?ModuleNo=34196Then get an adaptor
So rather than pluging the audio leads in to the tv just plug it straight into the headphones. Not sure how volume control will work. Ill just give it a try.
EDIT2, yes it does work, sound is at an okish volume