just make sure there not distorting if there not making a poping noise from maxing out you should be fine
i have 2 pioneer 10" subs not the bes on the market but they take 350 watts rms each and i was running them with 500 watts rms each i just had every thing turned down and they were fine
amp gain has no effect on power output from the amp. if the amp is rated for more power than the subs can handle, just don't turn the volume all the way up, and they'll never see the full power of the amp. set the gain properly to match the line pre-out voltage from your source.