I use a line level output. Before playing audio I must lower head unit volume to level 4 or 5. If I skip that step I risk blasting myself out of my seat!
Guess I overlooked the 12db boost before install. If a -12db 3.5mm inline attenuator can be sourced,I would be all over that.
For me the line level output is preferred,as it remains constant. The signal itself is probably cleaner as well,being at pre amp level.