If a Headunit puts out 2.2volt signal, and the gain (0.2v-6v) is set to arround 2.2v on the amp,,,?

well the gain should go from the lowest volt number to the highest. if you have a head unit with 5 volt then your amp can put out its rms at a lower gain then if it was a head unit of 2.2 volt and that helps your amp be more efficient and not have to work as hard. it does that because its a stronger signal coming from the head unit so the amp doesnt have to amplify the signal as much to get as loud. you can actually go over the volt of your head unit but you have to be careful because thats how you start clipping.

it would be easier if they had the numbers on there but you can use an o-scope and a test tone. or you can get one of these http://www.wccaraudio.com/distortion-detector/smd-... now when you use a tone there are a few different things you should know. a 0 db tone will set your amp up so you wont clip from any song, unless you are clipping from the head unit or the song is clipping. using a -5, -10, or -15 db tone will boost the song by the number so a -10 db tone will boost a song 10 db but be careful because a song i had peaked at 33 hz and was -8 db, i used a -10 db so that would mean it boosted it by 10 to a +2 and anything above 0 is clipping. so i was clipping on that song and had major voltage drop so all i did was edit the song and lower the volume some until it peaked at -11 db. but the db thing doesnt necessarily mean 10 db on a soundlab.