I think you will have problems with heat if you mount it under the desk as the heat from the xbox will be trapped. Why not build a shelf on the desk over the monitor?I understand where you’re coming from though if you look at the under desk photo you’ll see there’s adaquit ventilation under the desk coming from the front and rear from the pc. Mounting the Xbox above shouldn’t add anymore heat and worse comes to worse I have a flower fan right beside the pc I can always turn on.
It’s gettign the happy medium of mounting it low enough down so it’s not too squashed at the top of the table but also so it’s not to close to the pc and effecting it’s sit supply.
I had origiaonloy planned to mount it under the desk way down at the back of the opposite end (basically jsut underneath where it’s currently sitting) though I want to fit some sort of pull out keyboard tray now so I can move my keyboard from it’s current incovnent situation so that’s sort of gone now