Not what you want to here but the cheapest and easiest way to deal with the various noise you have is circumaural closed headphones at least when alone.
If by outside you mean out of doors figure out where the noise is getting through. If it’s the walls you’re screwed unless you want do some major work. If it’s windows you can do a couple things. Most expensive would be to replace them with double pane if they aren’t already. Double cell blinds will also help cut down on noise but these can also be pricy. Blackout/thermal curtains will help cut down a little noise. If you want really cheap and don’t you can do what I did in my apartment. I just cut some foam insulation panels to fit inside the window frame. I blocked out some noise and all the light.
Some of the noise is probably sneaking by the door. Some foam or rubber weather stripping can help here. Will also block light trying to get by.
No easy fix for the central air that I know of.
For the refrigerator about all I think you can do is make sure it’s not touching the wall. If it’s vibration rubber sound isolation feet might help a little. You could also try throwing a piece of foam insulation behind it between it and the wall. Not sure how safe that would be though.
Depending on the layout of the basement you might be able to use some heavy curtains to cut down on the refrigerator noise. I’m curious about it making so much noise. I hardly notice the one in my house and it’s just around the corner in the kitchen. Even in the apartment the only time it was an issue was when running the auto-setup on the Denon, I would unplug it just for piece of mind.
For the equipment you either need to put it in another room or in a closet/cabinet to dampen the sound especially the Xbox cause that sucker is loud. However, ventilation will be an issue if you use a closet/cabinet.
Again the easiest cheapest solution for your present room is headphones.
