Setting Gain, by the numbers

I have an amp pro going into a kenwood 802-5. PAC states the amppro has a 5v output signal and minimum gain setting on the amp is 5v. So technically, I should be running my gains all the way down, correct? Setting by ear, that seems to leave a lot of power on the table, especially on the sub. I can get the door speakers to clip by ear and have those backed off a smidge which landed me around the 2v mark on the dial. The sub channel I had cranked over to max, .2v, and couldn’t hear any clipping. I backed it down to 1v and it sounds great there. No smell or distortion when played up to volume 60 on jbl hu. Am I playing with fire here? Should I just get out the multimeter check voltage at rca? Maybe buy a cheap O-scope from Amazon? I have a very reputable A/V installer near by, considering running it over there and having them tune it with their fancy SMD tools. Not sure what’s the best route. I guess it’s a classic dilemma with this stuff, you hate to not optimize your equipment, but you also don’t want to blow it up.

 

I have the fancy SMD stuff but before I got that, I used my multi meter and set by the numbers. A little simple math can tell you how many AV volts you should be getting at the amp’s rms power output.
-Set the radio at about 75% (in your case, 40)
-Play a 1khz track to set my mains and a 40hz track to set my subs.

 

Continuing with Destin's post, check voltage on the speaker output side of the amp and not the RCAs.

Here's a chart showing your target output voltage. Use RMS wattage and not PEAK wattage of the amp.

 

Yes, thank you for the clarification!
You’re measuring the amp output and adjusting the gain until you get the correct voltage

 

and just to be clear-- you want to set the meter to A/C voltage, as you're measuring a waveform. measuring DC voltage on the speaker outputs will result in nearly no visible difference.