Am I going to lose two of my channels? How should I hook this up?

All aux-inputs are two channels (L/R) only.

The Empeg doesn't really have four channels. It's the same as every other car stereo: It has two channels that can be faded between front and rear. The only reason there's four outputs is so that you can control the fader from the front panel instead of having to reach into the trunk every time you want to adjust the front/rear balance.

Okay, there's also the ability to EQ the empeg's fronts and the rears differently, but you wouldn't be using that if you're feeding it into the Blaupunkt anyway.

So just choose one pair of outputs (either the fronts or the rears), plug them into the aux-in, and leave the empeg's fader set to "centre".

I can't help you with the details of the actual physical plugs themselves, as I don't know how things are connected.

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Tony Fabris