We don’t really have any recommended settings when using a subwoofer.  The crossover will depend on the individual size and shape of the room, placement of the sub in that room, and even personal preference. I usually recommend starting with the Crossover all the way counter clockwise.  Get the Volume close to where you think it should be for starters.  Then make small adjustments to the crossover and see how they sound.  Finally when making adjustments, assess them from the same spot each time, preferably from where you’ll listen from most often.