Single driver full range speakers

Try locating the SVS subs directly below or right next to the base of the TB's (then dial them in again).

Guessing that the TB's roll off rapidly @ around 75hZ in those sealed cabinets - making higher frequency bass fill from the subs directional.

DeKay

Tocaro are up to 3-way and without any crossovers. 
 

there is nothing which sounds faster, easier and more fun. A piano sounds like a piano, a guitar like a guitar

I have a pair of PearlAcoustics Sibelius single drivers speakers. Cabinet design is CRUCIAL: in this case a Voight tube. My personal preference is low clean bass, no window rattling onslaught. The Sibelius itself is perfectly fine (38 Hz, with 32–36 Hz -6 dB), but still added a REL T9 set next to one speaker. It is set at very low volume, don't remember cut-off (crossover) frequency. 

I love the coherence a single driver produces. The low bass has very little directionality, so a separate sub works fine. 

Many years ago I heard a pair of Ocellis speakers (don't recall the model) with the PHY driver. A high-efficiency speaker that sounded very natural and full of life. Don't hear much about them anymore. 

Cabinet design and amp are also factors in bass production. I have a set of full range speakers that I had connected to a Marantz model 8. The bass was thin and I had to use a sub to compensate. I started running them on another tube amp and now I’ve got bass in spades.