You can also use a different kind of steering wheel controller for a different kind of car stereo.
For example, you can control BMW radio with Resistive controller(Hyundai or GM).

For example, you can control the resistive controlled car stereos(eg. Sony, Hyundai radio) with BMW E39 controller.(BSGr is required) This is useful when you install an aftermarket car stereo.

Use a 3.5mm stereo cable to connect BSGr to Sony Radio.