Reviving an old thread, because I'm in the same boat - I have MIB1 High (larger screen, silver buttons on the MMI controls and Nav Plus system) but I want CarPlay (only for Google Maps and better control of my music through Apple Music). I was looking at the units from Bavarian myself (seems to be the ones most have gone for here?) but one thing strikes me as odd - when reading the description it says if you car has an AMI port, as mine does, I would need to purchase an AMI to AUX cable (at an additional £5, after buying the CarPlay unit for £219) but then doesn't tell you anything else. I contacted them and their answers/replies are, shall we say, less than desirable/professional. I asked if I need to plug the AMI/AUX adapter into my phone, and the reply was "you will need the adapter but it does not plug into the phone", so I asked what does plug into the adapter, and the answer was "plugs to AMI port"
Naturally, I realise the adapter plugs into the AMI port, I'm trying to find out what I need to do with the other end (the AUX end) of the cable - do I have to route it all the way to the glove box to plug it into the CarPlay unit in order to get sound or what (which is what Integrated Automotive explain in one of the links provided in this thread). I wasn't sure if simply plugging the AMI AUX adapter into the AMI port "triggered" the MMI to enable to AUX control in the MMI settings, so basically the cable was redundant, but it just needed to be plugged into the AMI port in order to tell the MMI to keep AUX "on".
I did buy the Carista dongle and downloaded the app, had a quick play with it but then sent it back after I realised you couldn't even get basic functionality (scan for engine codes if I get an EML) without paying a subscription. One of the things I saw in the Customisations part of it was AUX activation, which naturally I'd have had to have an active subscription to execute. I probably should have just bought the 1month £10 subscription, activated AUX (and a couple other things while I was there) and then sent it back. At least that way I wouldn't need an AUX cable running up the car to the CarPlay unit if that's the case.
I gather from reading this what once you're in the CarPlay side of things, you can't use the DAB radio side of the Audi system - you have to use a radio app/spotify/etc to stream music via your data connection. Kind of annoying as I was happy to (finally) get DAB when I bought this car, as the two routes I drive the most (usually twice daily) I lose cellular data for a good portion of it, and nd up sitting in silence waiting for the internet radio to come back! I'm also a bit worried this won't sound good: I don't have B&O (my A3 is poverty spec, and I think it's only got the basic Audi speaker system - no amp or sub) and it already lacks the punch that my Lexus used to have, I'm worried that with the reported sound degradation using this aftermarket box it will just sound poor. And I'm not sure that all this for Google Maps is worth it (but equally, it seems such a shame that with a nice dash screen - the 7" one too - I'd still be using Google maps on my phone screen). I'd like to go for an MIB2 High retrofit, but the cost seems too inhibitive.