Howdy DennisHi Wanacoop,
I have a Kenwood DMX125 DAB here with me and I will be very slightly, by 1mm shave some material away from the lower aperture edge to have the 'nose' of the Kenwood fit through. I can't control the exact dimensions the manufacturers make their units of course and this one is just that tiny amount too big!
Personally, for the last 6/7+ years, I've used the free Tune In app on my phone to listen to any of the UK's radio stations as they all broadcast online. I'd then Bluetooth Stream to the Parrot Asteroid Smart I had in my Touring, so I've never used DAB in my car. However, the DAB signals around the country are improving and reception in a moving vehicle does vary according to the signal strength at any given moment and the quality of the antenna. Ideally, you'd have one in the middle of the roof, but that just wouldnt look right! If a good proportion of your drives will have you listening to the radio, I'd say to get a good quality, short stubby type DAB antenna that has a short 2/3 inch mast that would fit where the OEM telephone antenna would have been on the top of the rear wndshield.
Other than that, there's no showstoppers in using the DMX125DAB. If your car has OEM Satnav, you'll need the extension harness from the back of the car to the dash area. If you're OEM setup is the DSP one, then ideally, you'd remove all the OEM modules and replace with a good 5/6 channel amplifier and upgraded speakers/sub all around.
Drop me a PM if you like about the potential routes you could take with your car. Plenty of information online with other owners and their audio upgrade routes too.
Looking to grab one of these from you! I sent you a pm, please reply before quarantine ends