You have NAV and DSP. That makes it very difficult. Do a search on this forum for Hualingan and DSP and you will get an idea if you still would like to do this change.
The way the audio system is build in BMW is that each component in this setup has to know the presence of each other. So, if you remove the NAV or the radio DSP amp will not stay on. The easiest way would be to replace the DSP amp with an aftermarket one.