/diy/ - Do It Yourself

I didn't see any kind of audio specific thread, but this is still electronics.

So I'm building the audio system for my 80's car and wanted a period correct head unit for it. Found the unit, restored it and it's running great. I still want a 3.5mm jack and bluetooth with it, though. Fortunately the rear of the unit has an aux port for a CD player (albeit as weird 8-pin din) and I have the schematics that tells me exactly what the pinout for it is, and slapping something in there would be fairly easy. The tricky part is most aftermarket bluetooth modules that are ready for install out of the box have their output at line level, and my head unit has a built in preamp that the aux goes through.

Is there a good way to reduce the line level down? I know it would be a bit redundant to drop and then raise it back up, but I'd rather have everything integrated and controlled from the main unit instead of having two units hooked into the amps.