High Pass Filter for Mains

In my speakers, the tuned port is not just low end. It's a tube that terminates an inch from the back of the woofer. Plugging it muffles everything. 

The Merchand filter is 24 db while HSU is 12. It is essentially a single cap for each channel. I was hoping for an off the shelf alternative to waiting a month. I'm impatient.

Thanks for the inputs.

I think I'm going with the Marchand balanced passive filters with a 80hz cross. It's $200 more but fits my connectivity better. What I meant about "a single cap" is its a single connection for me. Inside it's full of components. He offers 30 day returns so I'll order the sub when it arrives and have 30 days to evaluate. 

I'm just surprised with all the niche audiophile products out there, only one guy makes these. It makes me wonder whether this is an unusual endeavor in audiophileland. I've seen some previous discussions but no real conclusions. I'll report back when I complete the experiment. 

Thanks again for all the suggestions. I feel much better about Marchand and it's the right solution for my needs. I always prefer the simplest circuit with the fewest components. 

The SVS SB-1000 has dsp eq built in with app control. I definitely expect to utilize it. Otherwise I would just be duplicating my problem. If it works out, I would look to upgrade to a sub with variable phase. 

From 100hz up, my system is +/- 1.5db and sounds great. If I can get the frequencies below that to +/- 3db I'll be happy. 

@glennewdick 

I have 9 24x48x6 bass traps on the back wall and ceilings, and four 24x48x4 panels. They do a great job above 100hz. It's a small room and nothing is really gonna deal with below 80hz. I'm not sure this experiment is going to work but I won't know unless I do it. 

@mitch2 

What is the crossover point on yours? I need 80hz. Do you want to sell it? I ordered one today but it's four weeks out so I can still change my plans.