Ok. My head unit's rcas are 2.5v.
My sub amp has a sensitivity of 8v.

So would I be correct in having my gains to the higher side of the spectrum? like 1/3 to 3/4? I tried the "by ear" testing and to be honest I just can't seem to detect when any distortion comes in.. even at full gains..

 

I'd guess your gain control on the sub amp starts at about 500mV? Offhand I would say that you're in the ballpark at 1/3 to 3/4... sub amp can be a bit harder to set by ear, to a large extent you're level matching it with the other amp/headunit, while avoiding excessive distortion.

Make sure you're playing some dynamic music in which you'll be able to detect distortion... ie: put the 50 cent CD's away (not saying that's what you listen to).

 

For 3/4 overlap you'd want it a hair over 1/2 way.... However, if you arn't getting any distortion, you might as well crank it...

 

when they installed it they originally set the amp's gain at like 1/4. Maybe they were just protecting themselves from idiots (figuring i was gonna crank my system to the max). Right now I just set it to about 5/8 and there is no distortion.. but.. even if I set it to full gain's and put in a super bassey cd I still get no audible distortion.. but I don't wanna run with my amp gains at full all the time.. that just doesn't seem right.