I have a PCE 353 which I used to set up a pair of Wilson Benesch Torus Infrasonic Generators with their outboard amp/crossovers.
https://www.pce-instruments.com/us/measuring-instruments/test-meters/decibel-meter-kat_162375.htm
You only need to match the sub bass drivers to your main speakers 1kHz level using an appropriate test tone found on many reasonably priced CD demo discs.
Use your ears to fine tune to taste. It is not as difficult as many lead you to believe.
I hope this helps!
https://www.pce-instruments.com/us/measuring-instruments/test-meters/decibel-meter-kat_162375.htm
You only need to match the sub bass drivers to your main speakers 1kHz level using an appropriate test tone found on many reasonably priced CD demo discs.
Use your ears to fine tune to taste. It is not as difficult as many lead you to believe.
I hope this helps!