"Upgrading" my Funk Audio 18.1
So I've had a Funk Audio 18.1 (with upgraded 1000w DSP amp) for over a year now and it has been phenomenal except it does lack sub 20Hz performance (-6dB @18Hz). I knew going into the purchase at that time that I would be trading ultra low end performance for greater output above 20Hz, especially once I got into the 35Hz+ region. But now I want to try and get some very good sub-20Hz performance. Usage is strictly Blu-ray and UHD movies (no music).
Room is 24x14x8, closed off. I reached out to PSA and after talking with Tom he said their new TV36 would be a very good upgrade for >25Hz performance. However, the height of the TV36 simply will not work in my setup. He also thought that neither the S1811, V1811, or S3010 would provide much, if any, noticeable upgrade to my current Funk sub (though he did say the S3010 would provide some strong output down to 11Hz, but total output wouldn't be much more than the Funk overall). He did say that a used Triax I am looking at would be a very noticeable upgrade for me (his words "it would be closer to having dual S3010's").
For a budget around $2000 (can go up to $2500 max), are there any other subwoofers I should be looking at that would be a noticeable upgrade over my Funk 18.1?