I have a Kenwood amp 100x2 RMS, and 2 JBL 12"s that handle 125 watts RMS each. Should I have my gain at max then? Also, the low pass crossover should be on right, even with it hooked up to the Bose system with an adaptor? Thanks.

 

Most common settings is at half. Then play with it and adjust it until it sounds right. No one shoot me if I'm wrong, but as i remember from my sales and installing day, running an amps gain at max can damage it in the long run. Not to mention as you raise the gain, the sound quality goes down.

 

The gain should be set depending on your head unit, it is not a volume control! The proper way to set it is to get something that can measure the voltage output of your headunit and then match the amp to it. You could just use the RCA output voltage specified by the manufacturer of your head unit, but almost all of them lie about that number... Once you know the voltage output of the head unit, you can then match the gain on the amp to that voltage.

Now, if you don't want to buy anything, your beat way is to guess and listen. Turn the gain on your amp all the way down. Now crank up your head unit and listen for distortion on your front speakers. When you hear it, remember the volume it came at and never ever ever go above that volume! Subs tend to drown out distortion so if you go above that point you may not hear it and you'll be killing your speakers. Now, turn your head unit to the maximum volume that you will ever want to listen at (not exceeding the maximum volume before distortion you found above), and go back to the amp. Crank the gain up a bit at a time, shut the trunk and the doors, get in the car, and listen. Keep turning it up until you hear distortion. When you hear distortion, back it off a bit and you're set. If you can go all the way up without hearing distortion, well, it's there and you're just not hearing it. I would suggest not going over 75% if this happens.