Hi Tom,
There are numerous DIYs for this type of head unit upgrade. Assuming this unit is similar to the Eonon and Dynavin and Seicane units:
If you have factory NAV in your E53 you will need to run the cable to the rear under the spare tire to make the connections to the front mounted new head unit.
If you do NOT have factory NAV, your wiring is simple plug n play at the front, BUT you have some frame cutting fabrication things to do for the new/larger head unit to fit where your Business CD/MID unit is located.
I bought an Eonon GA6166 and my install is outlined here:
https://xoutpost.com/1100216-post170.html
That thread linked above provides a lot of insight on installing this "style" of upgraded head unit.
Good Luck,
Mike