do you have Nav? DSP?

if it was Nav, does your radio have round pins in the plug or straight pins? for the aftermarket radio to work with the steering wheel controls, the aftermarket unit should have an iBus protocol and hardware, and all BMWs produced from about 1996 to about 2007 or 2009 (X3 first gen and Z4 were the last iBus models) have the same iBus protocol, that has been well documented and hacked long time ago - there are aftermarket devices such as StealthOne, eLight, CIS-IBUS that take advantage of the iBus architecture... the newer bimmers use MOST protocol

can you post your aftermarket instructions? maybe scan them and post, along with your car's factory setup?