We are really talking about two different speakers here. I had the same Hsu sub and yes, it was a beast, providing very deep bass with slam factor. But, after messing around with it for a year I ended up realizing that I just did not like it. The only way to get rid of the port chuffing was to bung up both ports. Even then it was just too slow for my Snell D's and certainly for my LRS. I never tried it in a home theater setup and I imagine it would be great for that.
Enter the REL T9x and it was a whole different ballgame. For me, the REL is much more nuanced and punchy, quick and 'musical'. I will be putting another one in my system at some point in the future. Or maybe try a different sub for flavor - Rhythmik perhaps? But, not a Hsu.
Anyway, I can totally see where you are coming form OP. The REL will not do what the Hsu did. Not in a million years. But, I will say that I never turn the gain up on my T9x more than 5-6 clicks. Even in my long 40 x 15 basement the T9x gives me more than enough.