My R53 Cooper S has the unexpected bonus of the Harman Kardon premium audio system. While it has impressive power and sound quality (once you discover the hidden settings ), it's firmly stuck in the past with just CD and analogue radio. You can't change the head unit as the speakers are all wired to the 10-channel amp that lives in the boot, so new cables would need to be run from the head unit to each speaker, which would be an almighty faff. I wanted to add bluetooth so I could play my cheesy '80s music from Spotify, so bought a Grom BT3 which is a small module that plugs into the CD-changer port on the rear of the standard-fit Boost head unit. It allows you to stream music from your mobile, and make/receive calls via the supplied microphone. You can also buy another module that plugs into the Grom to provide DAB radio, USB, or iPod wired connections, I didn't bother with any of those, I just wanted Bananarama, loud. There are 2 versions of the Grom...