Oh is the remote wire simply any 12v live? It doesn't draw current, so can be tapped onto anywhere? I thought it might be some kind of signal, as I've always had them go to the back of the stereo.
If you're coming off the existing speakers for high level, why do you need a high to line level converter? It's got high level inputs?
When I was more into aftermarket car audio, I ran 4 awg power from the battery, underneath the car, properly cable tied etc to things and in through a removable drain plug at the bottom of the boot, as to not irreversibly damage anything. I'll do something similar again as the W204 has a drain plug at the bottom of the boot well too, under the spare tyre. Much better, neater and easier than running it through the bulkhead, trying to get it at the back of the passenger footwell, then all the way to the boot. My piddly little 3L V6 non-AMG mobile doesn't have the battery in the boot, so I'll resort to my old ways.
Yeah, I've still got my inline fuse somewhere.
Are you getting close to ordering the cerwin vega vpas10?