I can help with general tuning advice for your setup. Can you provide more details on the enclosure type (ported or sealed), desired sound characteristics, and any specific tuning frequencies you are considering?
What is the lowest frequency for the subwoofer or the range as stated that the subwoofer should be on? So nothing is coming out then no matter what tuning frequency you place it on. Start with 20 hz, then work your way up to 120 hz, and see if at every point of check there is static, sounds, or nothing. If there is some sounds at one point of the hz, then set the gain from there, Up, down, then volume control with the gain to set. To see if you got the correct sounds from the subwoofer. Fine tuning then the subwoofer and the amplifier to the subwoofer.