I have the above mentioned head deck running two headrest monitors. When I use wireless headphones with the displays, the sound doesn't get that loud. I thought it was the headphones so I used them in a Volvo stock setup and they got real loud. Long story short it's the Pioneer deck not putting out enough juice from the "REAR AUDIO OUT" jack. I hooked two other sources (Wii and DVD player) up to the displays audio input and the wireless headphones where loud. So I know it's not the displays.
I've searched all through the manual and I see no way to control the volume on this jack, but it sounds like it's not pushing the normal voltage that it should be. Anyone have any experience with this? I don't want to/shouldn't have to buy a line level booster.