A radio upgrade would be a swap to a new one. However, a 2002 radio is pretty new in the grand scheme of things, and I would have expected it to support an in-dash CD player. This one is officially a mystery to me. It might still be worth a radio upgrade and then sell yours on something like eBay. The net cost would not be that much.

I have to confess I don't know how the CD and tape work. Are the CD controls internal to the monitor, or does the track advance button press go to the BM24/BM54 over iBus, then back to the monitor from the BM24/BM54 as a command to activate the transport?

Perhaps somebody could tell me, will the 16:9 monitor that I have removed from my E46 fit into an X5? I have somebody who wants to buy it, but I dont know if the screen is the same part or not?

No, it will not.

X5 screen is totally different with a differnt angle LCD and all.

E46 screen only fits E46, same with E39.

It's all I-Bus.

The CD player and monitor/buttons are both independent components connected to the I-Bus. The track change buttons send instructions to the radio module over the I-Bus. The radio interprets them based on context and then sends commands over the I-Bus back to the cd player. The monitornand cd player are more-or-less electrically independent, but happen to physically co-located in a common housing.