In short you change hub to dual but with compatible to AA, here are my records, all compatible
156138299 NAFTA 156143958EMEA -> 156147799 -> K6QW48DX8AC -> K7AQ67DX8AA
then you go to proxi, right Alt+C on last tab.
byte 115 must be 0x15 (dual with aux), so if different change it (single are 0x14)
byte 157 you need to set lowerst bit, so e.g. in EU GIulia 0x30 change to 0x31, in EU Stelvio 0xB0 you change to 0xB1 - this adds mirroring function
byte 161 in both cases change to 0x3 - this allows AA and ACP
byte 163 I do not think needs change, but I set it just in case to what I had with stock AA/ACP to 0x02 (giuliaforums said about 0x1A which acoording to my proxi info has no function in these cars)
giuliaforums also said byte 174 to 0x02 but in my stock car I had this 0x00 as well my proxi records have no funciton for that byte in pre-facelifts. I do not set that one to customers and a few activated sucessfully
after you do change, OK, then run proxi, when done, power down for say 1.5minute so all dash and radio fan (later) gets quiet, then after this you can go to Witech2 and activate in ETM Carplay option which enables both AA and ACP.
All parts can be purchased here to do the job:
Alfa Romeo Giulia/Stelvio OEM 2018 + infotainment head unit.
alfissimo.com
alfissimo.com