Welcome to the forum!
What speakers and sub are you using?
My initial guess would be that the speakers were set to "Large" (probably by the auto set-up routine). If that's the case, set them to "Small" and try a crossover frequency of 80 Hz to begin with.
Also, have you calibrated the sound levels for the speakers and the sub? It's also possible that the subwoofer volume is just too low.