Well, i see tutorials all over the Internet about how to use a PC PSU to power a car amplifier in a house. I wanted to try it but it seems I'm fresh out of PC PSUs... I do have a lot of old xbox's that gather dust. So i improvised. It really wasn't that different than a PC PSU because basically, the old xbox is a PC.
I'm not responsible for any harm you do to yourself, or your xbox or amp. Okay so here we go.
That's not the speaker rattling btw, and it's turned way down but still hits pretty good throughout the house.
And please remember to have the xbox completely unplugged while working on it. Even if it's unplugged the PSU can have power built up it it and it can shock you. I learned that the hard way.
You should be fine as long as you don't pull the PSU out.
Things you need
-Basic tools for the wiring (cutting, splicing, etc.)
-Xbox (or just the PSU..)
-An extra 4-pin molex cable, if you don't want to cut your xbox cables up.
You can also use a 4-pin male to 2x female if you want your xbox to be fully functional at the same time.
If you have an extra female 4-pin, i would recommend using that, so you wont have to cut the wires that are on the xbox. You can also used a splitter like in the second picture and have one end go to the amp, and one to the HDD to retain full functionality of the xbox