I've read up on how to do it by ear on this site, but a couple of things I don't understand still:
1.) Where should I set the "Sub Level" on my head unit when adjusting my amp's gain?
2.) Do I need to adjust my stereo's DSP at all before adjusting the amp? (I'm sure I don't, but there are a few settings that do effect the sub in there, such as "Bass" and 50Hz on the 7band EQ)
3.) Am I right to turn the bass boost off on the amp, turn the stereo up 3/4 volume and turn the amp's gain up until the sub distorts, then turn it down until it stops distorting?
4.) What should I have playing in the CD player while adjusting the gain? Will a normal "heavy bass" song suffice? or should I use some sort of test tone?