Just got my dayton sub in.... Onkyo tx-sr503 polk r15 front and rear, csi25 center, onkyo has choice of 80 or 100 crossover, all speakers are set to small. sub has two dials, gain - min/max and freq - 40-180. where in the heck and how do I try to dial this thing in? the r15 fronts will be replaced with a pair of r30's in a few days, how will that change setting them up?