Forky...I think the question is "what are you asking a sub/subs to do"?
From just a musical standpoint, with almost all bass being above 50hz.....are you asking the subs to....
1. Provide bass below 50 hz that your speakers can't do
2. Provide bass below 50hz that the room is stealing
3. Augment already good bass below 50/60 hz just to add some punch
5. Help the mid bass about by running dual stereo subs and crossing over in the 80-120 range
These are just a few of the possible combinations....but until you can answer them, relative to your chosen speakers and how they perform in your room, you will just flail around.
In my case....M3 Sapphires....huge room, 1200 sq. ft....the Sapphires have really good toneful and punchy bass down below 40 hz. I also have a good 15" sealed sub...Power Sound Audio S1500...no remote, no PEQ...no fancy anything...but great sound....so, if I turn it on, cross it around 50hz....resist any temptation to turn it up so that it overpowers the great sound the Sapphires put out...what I get is a slightly augmented bottom end...with just a little more punch...most of the time, I have it off, I'm not looking for a "nightclub" type of sound. Most of the time, I have it turned off.
Also, if you are just looking for augmentation down in the 50 hz and below range where the music doesn't really have much tone, I'd say that anything REL is going to work...but you are way over paying.
So, what are you asking a sub/s to do?