I see what he's trying to say. I think he means he's got 1 set of RCA's going into his amp which runs his 6X9's, on that amp there is another set of RCA outputs so you can "daisychain" another amp to it. It should work with no problems, only thing is you might lose the subwoofer control on the head unit if it's got one. In my car I have 2 sets of RCA's going into 1 amp (so I can still fade from front to rear) and on that amp is another RCA output which is connected to my sub amp. Works fine! If your sub is producing sound, then it works.
thats just personel preference really you can turn them up or down as much as you want really but the higher you have them the less life span your sub an amp will have because it will be working harder