Thanks for the kind words, gentlemen.
As I replied to his inquiry originally, the difference in cost covers installation parts, vehicle-specific parts beyond the Technic HiFi harness, wiring and cabling, technical support, and authorized warranty support. I neglected to mention that, of course, our sponsoring E90Post and M3Post isn't free, either.
Back in the day, when Technic and myself and a few others were the initial folks pioneering audio upgrade research and testing in E9x vehicles, the way he's talking about doing it is the way we had to do it. I would be somewhat of an ass to say that he doesn't get to do it the way I did, or that many of us did. Of course he can. In so doing, he will be using information that I and others provided in the past, but that's OK, we all put it up there to be used.
On the other hand, I can't begin to tell you how much time - and how many potential errors or mistakes - we are saving any for install project, with the collection of parts and adapters and interfaces which we provide. We offer a product which many experienced and knowledgeable folks have found to be a good value.