gains are not volume control... They are used to match the input voltage, when the amp's 'gain' value matches the input signal, you get max output at max input (if you have a 4 volt preamp out and the gain is at 4 volt, when your stereo is pushing all 4 volts on the RCAs, you have max RMS from the amp).. Turning the gains up 'magnifies' the input voltage (kinda, not really but work with me).. you are putting more than if the system was running 'nominally'.. I'd immagine that you had the gains up so high that the amp overheated and shut down..
There should be a volt reading on the gains some place (or in your manual?), set it to what ever the preamp voltage for your HU is listed at, no higher.. (well, maybe a little higher so you don't have to have the HU all the way up and into distortion.. but not much higher)
Gains can also be used to make sure your amps don't put out anywhere near full power.. if I set the gains to think I have a 10 volt input but only run 4 volts in, I can never match what the amp is thinking is full power and the output will be much less than 'nominal'.. This is how I'll have amps that drive a LOT more than whats needed to match the rest of my system..
Hope that helps (and is mostly right, I just learned some about the details of gains from Jmac and hope I didn't get this wrong.. I also didn't want to get to technical in case you don't care the whats, just the fixes and whys..)
(1) Alpine CDA 7892 HU ($214)
(2) 12" Pioneer Premier 1241DVCs in sealed MDF box (gonna glass them eventually) ($69 each)
->removing.. ->(2) 10" Pioneer Premier 1041DVC's in sealed MDF box (gonna glass them eventually) ($59 each)
(2) Lanzar Vibe248 1200 watt 2 chnl amps ($119 each)
It's bump'n GOOD!
You can lead a horse to water but you can't make a moron understand...