nl4jy: Yeah it's a slot-load. It's a tight fit up there where it is, but you have plenty of room to get the discs in and out.
That is a good looking install. I have a favor to ask you -- Is it possible for you to take a better picture of how you mounted the case in the trunk? Mine is not secured at all and I'm trying to figure out the best way to mount it. This is not a good thing in an M3!
1) It is easy! The amplifier does not actually turn on and off via I-Bus messages (in the e46 at least.. cars with DSP may have to power the amps on with I-Bus) -- It powers on and off via a remote 12V feed like any aftermarket amp. The power wire is the 'antenna' wire on the radio wiring harness. I just wired the 12V 'antenna/amp turn on' to the 12V ignition wire, so the amp is on whenever the car is on. I will wire it to a switch at some point so I don't have to power it during things like racing events. Next, you need something to convert the unbalanced audio from the computer to the balanced audio that the H/K amp needs. I used a Peripheral Electronics VEN4.
I will try to write a good guide on this in the next few days as a lot of people have asked me about this, and there is not much information on the net about it.
2) In my E46, the OBC display is in the instrument cluster (IKE), so I don't have to worry about that. I don't think BMW ever sold cars with the radio you have in the US, so I'm not familiar with it.. You might try unplugging your radio and seeing if maybe the OBC works on the instrumetn cluster with the radio disconnected...
You cannot access temp/fuel/engine information via I-bus. You can get engine information via OBD-II, though, which is maybe what you want. There is an OBD-II forum on this board that discusses that. I have not yet plugged into OBD-II in my car.