That or use an outboard crossover like this from MTX thats an ebay auction for $30. Nothing from Boss, Autobahn or anything like that unless you enjoy noise being added into your system.
So this kind of sucks, but would the best bet to keep your car radio for the preamp?
I actually got an idea about how to deal with the volume issue, but I do not have time to play around with this now. The idea is not to control the volume of the device, but to apply the volume control as a custom filter on the audio data stream. It will require changes in the application to make it AU-enabled but once this is done, creation of the appropriate filter should be a piece of cake.
Hey Jirka are you working with QCar in Cocoa?
Audio Hijack Pro.... is perfect for capture the stream audio from any application.
I use this for change the sound. Not equalizer or other strange things, but for Vacuum tube sound.
The audio interface that i prefer and use is the RME FireFace 400... nothing else meet this audio object...
Edirol UA-1EX - It's from Roland (as in Roland professional synthesizers). It's USB so you bypass the so-so quality "Line Out" earphone jack.
Add a AudioControl Epicenter and AudioControl Three.1 plus subwoofer amp and up to 2 other amps for front & rear
The Three.1 gives you a master volume control from the dashboard, as well as subwoofer control, balance and fade.
See my CarPC specs for details