yours.
But anyway, factory EQ can be accessed by holding down the "P.Scan" and "5" and turning the HU on. You can adjust bass, mid-bass, mids, and highs independently for front and rear. There are different settings that work well depending on if you have the Bose system or not but I generally turn the bass all the way down on the front and the highs and mids all the way down on the back to improve imaging and overall SQ. If you will use aftemarket amps, set it flat.

<center><img src="http://pictureposter.audiworld.com/66252/a4_bose_amp.jpg"></center><p>
on the back of the HU.
The amp is in the trunk as shown above.
Don't set it flat it'll sound dreadful unless you are installing your own equaliser between the HU and amp.

when you say flat you mean make it all zero? or make it all low? what you mean set it flat?