Let's just focus on the AC version for now. If we can get that working, the car installation will be next.

For this, I assume that you have a power brick / transformer connected to the power input on the player. You should have your line out jacks connected from the player to stereo or amplified speaker inputs. For AC use, set the volume to zero db - this is the standard "line level". Your EQ should be flat and your loudness set to zero or off.

Do you get any sound when playing a test track? Do you see any signal on the visuals (like one of the spectrometer ones)? Does it look as if the track is playing normally, counting the seconds, etc?