Just thought I'd add my recent experience of changing the Chorus radio on my 2011 A3 Cabriolet with something more up to date. The sound from the radio was pretty feeble although the sound from the CD player wasn't too bad but some CD's were skipping so time for a change.
I bought a Pioneer SBH-EVO64DAB double din radio as the replacement and used the A3 fitting kit from Halfords. The hardest part was getting the cage into the space vacated by the Chorus as the cage width appeared to be greater than the space but with a bit of brute strength it eventually went in (unlike the video on Youtube where the guy just slides the cage into place as easy as pie).
The new radio came with a USB cable, a GPS aerial and a microphone cable and these had to be threaded through into the space behind the radio first. The USB cable and GPS aerial went through to the glove compartment and the microphone went through to the drivers footwell via a gap and attached nicely to the side of the footwell, out of sight. I had to undo a few bolts on the glove compartment first to enable some room to thread the two cables through.
Before pushing the radio into place I had to push all the wiring down into the space behind to enable the radio to fit.
I'd thought about the aspect of the DAB radio aerial beforehand and didn't really want a windscreen aerial. I'd read that the A3 AM/FM aerial was in the windscreen pillar. I eventually found a post somewhere on the web where a guy had used the original A3 aerial for both FM and DAB by using a splitter so I decided to give that a try and bought one on ebay for about eight quid.
So I wired it all up and got the radio in place. This radio comes with wireless Android Auto and Apple Car Play and can display Waze as the Satnav. After pairing my phone with the unit, the satnav worked perfectly with the GPS aerial just sitting in the glove compartment and the hands-free phone works perfectly with the microphone in the footwell so no obtrusive wiring around the dashboard, everything is hidden.
However, I was disappointed with the radio reception - no DAB and crackly FM. Disaster! So I took the radio back out and had a good look and realised that I hadn't connected the blue wire from the aerial booster to the remote wire (blue with white stripe) so there was no power to the powered aerial amplifier. After joining the two wires - success - perfect FM and DAB reception without a dedicated DAB antenna.
The only minor disaster was by taking the radio back out, the plastic trim round the radio that came with the fixing kit lost two of its four spikes that fix it to the cage - they just snapped off. So at the moment the trim is just attached by the last two spikes and I've just ordered a new piece of trim. So if you're doing this, be careful attaching the trim.
Hope this helps anyone thinking of adding an aftermarket unit. I'm really pleased with the one I bought, I've now got FM, DAB, Satnav, Hands-free phone, wireless functionality, all my music files instead of CD's and Alexa if you have it plus all the apps.