i facing same issue like yours last time ..
these are my research / advice from sifu ..
1. Some sifu able to relocate your current HU to other location, so the display can still remain (the button to control the screen, not sure what car u having). So they pull another power source and link your speaker to the new HU.
2. There are some China OEM HU which able to remain your car existing funtion (the button function i mean), of course the sound quality is still acceptable la .. Some come with android so you can install your waze and other apps. Of course you need to find specified model which fit to your car (easily can get from taobao). And normally they come with the converter (dono what it called la), so no wire cutting.