Probably neither are an option.
Adding an aftermarket head unit will loose the car functionality controlled through the Rlink2.
Buying a second hand unit, the Rlink2 will be coded and locked to the original car as a anti theft precaution, and can only be turned off in that car.
Apparently this can be done in ddt4all, but looking at the settings ddt4all says once set it can’t be in set.
The theory is to unattached it from that vehicle by removing the vin settings, Put it in an engineering mode, it will then be able to be transferred to the new vehicle which the settings and new vin can be set.
the alternative is a brand new Rlink2, comes ready to set up, dealer fitted is around £1200, then you still have to code it for car play and add USB ports.