Intergrating a powered sub..Question

Just found out i need a pre/amp separate to intergrate a sub properly. So thats that...But then why does a sub amp have a vol control...what a minute, I think that other advice may be wrong. Anyone?

I have the Cayin. However, I see an OUT on the Jadis intergrated. So maybe I could use that preout...to...another amp(my old Rotel) and get a basic Marchard XM9, and go from Jadis preout to Rotel, with the Marchand hooked up to the Rotel, then the sub(w/o KGamp) speaker wires hooked up to the Marchand. Correct? Or go from Jadis preout to a KG5230 amp on the sub cabinet? Confussed...Basically I'm looking for the cleanest 20-50hz's. I guess there are 2 or 3 ways I could do it. Not sure if the KG is a real good music sourse.

Yes but the advisor says that the preout on the Jadis(forget the Rotel) is not controled by the vol on the Jadis, thus you cannot get the proper vol to the W26. But to think of it, most/all subamps have a vol control. So I think the "advisor" is wrong. You can adjust the vol of the bass as much/little you like. Does not have to match EXACTLY the vol of the main amp. Though obviously a vol control on a preamp (separates) would be ideal. Thus the subamp, like you say acts like a preamp AND xover all in one. I may go that route. I'm just looking for alittle filler, as the W18's only go down to 40hz's. Is it worth the $700 investment building the W26 as a woofer separate(not a true sub)?? ..just to get some lower fq's?? Not sure yet....