Little help with REL subwoofers, please?

I'm not especially knowledgeable about subwoofers and I'd appreciate some advice. I've got a pair of Magnepan 1.7i placed in a small (long, rectangular) room. I had a hefty JL sub that shook the house but that I could never fully integrate. On a whim, I switched it out for a pair of the diminutive REL Tzero subs and the sound is vastly better. On some music, though, such as classical organ, I miss the growl and thunder. I don't feel like I need to boost the "upper bass" and I definitely don't want to muddy things up; it's really the deep rumble that I occasionally want.

If it helps, I'm thinking of a piece of music like Max Richter's "On the Nature of Daylight," which about halfway through delivers a broad, deep sweep of musical sound that I want to *feel.*

I'm mostly pleased with the setup and I don't want to reinvent my room's wheel or break the bank. And I'd like to stay with at least two subs and likely stay with REL. So I'm thinking I might: 1) add a T/9X or maybe a T/7X and perhaps keep the crossover low; or 2) swap out the Tzeros and replace them with a pair of T/7Xs. For now, a pair of T/9Xs is a budgetary stretch that I'd like to avoid (and it is a small room).

Would it be weird having two Tzeros combined with the much bigger T/9X? Would the T/7X produce that deep, enveloping bass? I'm not particularly good at reading specs but -6dB at 30Hz doesn't sound especially deep to me. (The JL was -3dB at 23Hz.) Or am I misunderstanding how bass works and would a T/7X go plenty deep in a small room?

Thanks and Happy New Year!