Be careful - there is lots of potential for groundloops in this. Also, any switching of 240V should be made by someone who has experience both with wiringi and 240V mains - safety issues especially.
I would use a headphone wich for each headphone so either may select any source. As for switching th rest, its a job that requires a litle thought. I have seen similar boxes at audio shops to switch between generic appliances. I am sure it would handle your games, TV and amp as these are hardly unusual. You might spend a similar amount as you would on components and come away with a product that isn't just safe and well designed, but offers more than what you are askikng for.
I believe in buildikng my own stuff but there are times when products on th market are simply cheaper or better and worth th expense. Look into this before committing youself. And, again, beware the 240V. One mistake can be very expensive, and maybe fatal.