Not often I can make a contribution without asking but here goes.
Purchased a NZ new 2005 e60 530d with a CCC MASK Idrive system in it with the 6 disc changer, unfortunately it didn't come optioned with bluetooth nor could you easily retrofit aux.
Options were: Dension Gateway 500s for a small fortune, or
https://www.ebay.com/itm/Bluetooth-Music-Adapter-BMW-5-Series-E60-E61-i-Drive-Business-Professional-M-ASK-/222297726822
I was a bit hesitant when it arrived, did plenty of research that indicated i'd need to code in MP3 and enable the MASK system to see the new functionality.
Turned out, hooked into the cd changer 12v, plugged up the fibre connection and after a couple of minutes for it to recognise the new functionality i had spotify working over bluetooth, aux in, and although it didnt show it in the communication screen it allowed me to answer a bluetooth phone call. No coding necessary. Although it just shows CD1,2,3 etc instead of the track names/artists, but the steering wheel functions work just like factory.
Not bad for $200 landed either.