Useful info on this forum, thanks to all that have posted. I decided on an Atoto F7xe, and also that my wiring skills weren't up to scratch, so asked the company that did my conversion to have a go. Absolute champs, did it for sixty quid (so £310 including radio). It works perfectly (in a 20 series Vellfire, non-amplified system), connects to Android Auto on my phone as it boots up, shows rear view from camera, and has DAB+, even comes with a mic. I had quotes from car radio specialists for fitting this system ranging from £780 upwards, so it's worth just phoning around for a cheaper fitter.