[full foot notch]

if ya want, ya can set your gains properly with an oscilliscope or a multimeter, your gain is there to match the "signal strength" of what the radio is putting out/producing, what is meant by signal strength, is more the line output voltage, its hard to describe in words, but as i could put it best in my words would be, say your radio puts out 7vDC for line voltage in the preouts, well the gain would be adjusted to match that 7vDC , but if you had another radio (say a low end pioneer) it may only put out 3vDC, and so the gain would be matched for the 3vDC output

my quick technique if in a hurry is to adjust the gain at listening level to any audible distortion can be heard and then back off 1/4 turn, its only best to do with a trained ear, if ya know what i mean, but if you really dont know what your doing, take it to a car audio shop and they may do it for you for free or maybe a $5 tip to the guy