I am looking at buying the XPA -5 barely used from an individual, and looking at the specs it says S/[email protected] and at .1percent [email protected]/1meter. Isn't 97 kind of low on the noise floor? Would I have to turn down the gain on my sub to keep any hum from being introduced? And in doing so, not get the full wattage from my sub amp? I was told years ago when looking at specs on amps, to keep it to .01 percent which is not audible to the human ear. I would like someone to she'd some light on this matter, please.