Suitable Low Frequency X-Over for B&W Matrix 804's

Hi there I am almost done modifying my 804's, I have really just given the drivers a once over and there in great condition as well as put mundorf supreme caps and a better resistor in the crossover. The cable inside is actually really good and built just for the Matrix series.

Any way the drivers use a linear suspension in a 2.5 way configuration. I am going to install a capacitor in between my RCA's and the input to act as a crossover as oppose to using a active crossover and adding another link in the chain. So I am not using a passive subsonic filter for reference.

Thanks a million
Toby