Z3 Amplifier upgrade question

Lots of people use aftermarket amps with the Z3 headunit. You have to choose the right amp, however. Some amplifiers handle "Line Level" inputs, or levels that are already strong enought to run speakers. You can connect those amplifiers right into the speaker lines. Others require pre-amp level inputs, which are RCA connectors in the back of modern head units. The advantage is that, since the signal has not already been amplified, it has lower noise to the input. Then most modern amps can handle either level either by changing a swithch or automatically. Plus, if you have the wrong configuration, you can buy adapters to match them.

The BMW head unit has a pre-amp level to the HK amp. Just about any aftermarket amp will work just fine if you connect to those wires. Just don't choose an amp specifically made for line level. You will probably have to install RCA connectors to the BMW wiring or choose an amp that has screw connectors for the input wiring.

A bad way to do it would be to connect a line-level amp to the output of the HK amp. Then you would be amplifying the already bad 10% Total Harmonic Distortion.

An even better choice would be to replace the head unit with a modern one that has an ipod interface, etc. Then run a three-channel RCA cable from the pre-amp of that to a new amplifier in the trunk.

I have the HK system. I have purchased an Audiocontrol LC7i to accept the 4 channels + sub from the factory CD43. Just to be clear, the INPUTS to the Audiocontrol will be the wires labeled "left back in +/-, left front in +/-," etc.

These inputs are from the headunit and are completely unfiltered, right? I will use the crossovers on my new front component speakers to do that.

Then I will connect all the wires like "left 1" +/-" to the amplifier outputs, since I am reusing the stock wiring.

If that's all correct, I think I finally understand how the wiring in this works!

I guess you could do that, but normally the crossovers go between the output of the amp and the speakers.
The head unit output correspond to amplifier inputs for each channel.
The amplifier output can go to the speakers (for broad-frequency range speakers, such as the rear speakers). For component speakers, the amplifier output goes first to the crossovers to separate the frequencies into low frequency for the mid-range speakers (usually in the footwell) and high frequency for the tweeters (usually in the door).
You will supply your own wires between the amplifier and the crossovers and connect to the existing wires everywhere else.