Need help soldering controller!

I’m building my arcade cabinet control panel and am incorporating an xbox 360 in there. So right now i’m trying to connect the controller to the buttons on the arcade panel. I’m having trouble figuring out where to solder the wires to. I’ve looked at the diagrams on slagcoin and have read countless number of forums and threads but still need help. I have an old wireless xbox 360 controller that is not considered common ground. How do I go about soldering this type of controller? This diagram is very confusing to me
Can anyone dissect this diagram and put it in words I can understand for me? I would really appreciate it. Thank you all for you help

First off, its much better if its a common ground controller but if you’re using this controller be my guest.

Blue circles indicate signals, in other words where you need to solder to to access the button signals.
The color of the Letters indicate what ground it is common with. In other words, using that diagram, Up, Down, RB and A share the same ground connections and you only need to solder 1 ground for those four inputs. Same with X, Y, B, they use the same ground points and so you only need to access one ground point. The same color as the circle in the diagram indicates the ground point that is suggested for use with that set of buttons. In other words to sum it up for you.

Up, Down, A, RB share the same ground
X, Y, B, share the same ground
LT, RT share the same ground
Left, LB, share the same ground
Right, Back share the same ground
Guide, Start share the same ground

In other words, you will be soldering about 21 wires to the board, 15 for signals and 6 for grounds.

Someone correct me if I’m wrong here

Makes a lot of sense. Really appreciate the help man. Thats what I was thinking but I wasn’t sure since I’ve read in other places that each button had its own ground. Thanks for clearing that up.