No high pass filter on sub woofer!

Another digital option:
http://www.dspeaker.com/en/products/20-dual-core.shtml

If you have a modern integrated with no way to separate the preamp and power amp sections, while they operate simultaneously (as is the case with most modern integrateds) your option is the passive filter between amp and speakers. Certainly not an ideal option. 

If you are open to a digital crossover these two pro pieces from DBX
are very flexible...They have an iOS app so you can make adjustments from your iPad/iPhone. You can choose different crossover slopes, it has a 8 bands of parametric EQ so you can notch out problem frequencies...https://dbxpro.com/en-US/products/driverack-venu360https://dbxpro.com/en-US/products/driverack-pa2
You can find them on e-bay...The Venu360 uses 24/96 in the a/d section for the crossover. I use the PA2 in my system and I love it...I am using for just the low pass to my two sube...but the flexibility is great.

helomech's suggestion is NOT a line-level filter. It is designed to be installed between the power amp and speaker, not the best way to do the job.

https://www.parts-express.com/80-hz-high-pass-8-ohm-crossover--266-458

Dear @donvito: In my first hand experiences the best way to do it that between other things improve transparency and system resolution is these:

https://forum.audiogon.com/discussions/speakers-speakers-and-more-speakers-but-need-bass/post?postid...

that's what I did it in my system even that my subs comes with high pass filter :

https://forum.audiogon.com/discussions/speakers-speakers-and-more-speakers-but-need-bass/post?postid...


Regards and enjoy the MUSIC NOT DISTORTIONS,
R.