Sony Drive S Selectable Sub-Out?

Ok so I play music using the "audio" mode but my friends accidentally messed it up and now the audio doesn't work when I play it from my iPhone and when it does work it doesn't go at the same loud volume on "tuner" mode. How can I fix it to stay at the same volume as my tuner?

The title of your question mentions "sub-out", yet nowhere do I read a question regarding the sub-out.

Next, you mention the audio doesn't work when you play from the iPhone, yet state "when it does work". Well, wouldn't "when it does work" be "never"?

Regardless, turn off the unit and hold the volume know down while the unit is off. You'll be rewarded with a variety of options which aren't accessible when the unit is on. One of them is the Aux Input volume level option.