Is it possible for one of the RCA pre outs to go bad on a Head unit? Or would all 6 RCA hook ups go bad at one time?

Reason i ask, is i received my new amps and when i go to adjust the gain there is very little to no change in output.

I tested voltage to the amps, Grounds, etc...

BTW these are my Sub woofer amps... My 4 channel amps for the mids/highs works fine...

 

There are several things you should double-check on some equipment. First make sure your subwoofer volume on your headunit is at neutral, low pass filter turned off if you have one. Also, double check that your fader and balance are both neutral. Second, make sure your amplifier is set to all pass or just low pass, and make sure that if it has a sensitivity switch that it's set to the correct voltage. If you're still getting close to no audible difference in gain variance, then hook up your subwoofer amplifier to the rear channel RCAs. If you get a drastic change, then the subwoofer RCAs have a problem. But if the gain adjust has no audible difference when hooked up to the rear speaker RCAs, then it's gotta be a bad amp. There are just lots of variables in this situation.