Yes, the DSP takes just front L&R but the HU also has outputs for rear L&R, if you want those you just need to add connectors/wires.

I'm not sure if battery unplugging in necessary, it may be that the i-bus resets after a while but still, unplugging the battery is a quick way of doing this. If you wait until navi computer shutdowns, there will be no problems or lost data.

For quick test you just need to unplug the 18 pin audio input connector from the DSP amp, i-bus is also in that same connector and disconnecting i-bus from the DSP amp makes the DSP disappear from the whole system.

I'm describing just general things based on BMW technical documents and BMW messageboards, my own experience is from E39 which I upgraded from Hifi to DSP amp from -02 and radio from -04.

Have you read these?
http://www.unofficialbmw.com/e39/ste...reo_posts.html