aftermath

I searched the archives and saw that some people had trouble with the Blau adapter (lights not working, trip computer going out, etc.), but I could not find a good description of how they solved the problem. Let me start by telling you what I'm planning on doing:
4-ch amp to power front and rear door speakers
2-ch amp to power 2 subs
So I'm not worried about losing the stock sub or anything, but I would like to keep my trip computer and the lights for the stereo buttons. I'm having the work done at a local shop (I don't trust myself) and they are using an adapter similar to the Blau (it was fabricated for a Porsche, but it should work). What do they need to do to avoid the problems?
Thanks a ton.