This isn't my car but it shows what my center console looks like:
The large lower rotary knob on the left side controls the stereo volume. You can also push it to turn the stereo on and off. After installing an aftermarket head unit this knob will become useless. Would it be possible to somehow mount the audio adapter behind it and rig it so that the OEM knob controls the audio adapter? Both knobs function the same way so I would think that somehow it could be done.