In my 2012 mdl II, I have my iPod in the usb port, it all works fine, but the sound is 10 points higher than the radio or my iPhone BT/usb direct.My HU setting is like 35 for everything but the iPod, the iPod setting is 25, for the same sound level as everything else. When I use head phones on the iPod outside the car, I can almost hear it, so its not blasting like it does when I change from radio to iPod in the car. Anybody else have this issue?
I'm guessing your headphones are fairly inefficient, and it takes a higher volume level output from the iPod to drive them than it does to provide the line level input for the head unit.
Follow up.... I went into the iPod setups and adjusted the Max volume settings, So I can hear it fine with head phones, and when in the car hear it about the same as the radio, Looks like maybe the HU uses Max volume settings for playback, cant say but it is better.