Low pass filters

[mic d]

I have an alpine hu it has a low pass filter i also have prec. Power amp it also has a low pass filter i only need 1 how do i cancell out 1 of the 2

 

[Slo-Sho]

You can set the amp on full pass and use the HU. If it were me though, I would run both low pass at around the same frequency and at -12 db (preferably -24db) if you have the capability. Redundant filtration, if you're sending a low passed HU signal then the amp will also low pass filter that signal.