I think SVS generally uses more sophisticated drive units. Their previous 2000 model, for example, used a version of the venerable Peerless XXLS12 drive unit. That's the same basic design as used in Genelec's
most powerful sub to date, as well as a number of "audiophile" brands. Some of their more expensive ones have underhung motors, which are more expensive to make (the top plate is much thicker than an overhung driver). That doesn't necessarily mean much, but IMO "musicality" in a subwoofer comes from having smooth extension well above the intended passband (making the crossover easier and more predictable) and no or benign port resonances. The XXLS12 is good to 500Hz, give or take. For single-sub users SVS has an app that may be of use as well. As a multi-sub guy I see that kind of thing as unneeded latency, but there are undoubtedly more single-sub systems than multisubs systems out there.
Aside from that, REL's connection scheme is antiquated, wrong-headed, and counterproductive. You may in fact want the subwoofers and the mains overlapping (presuming no automated room correction in play - none of the current systems except maybe RoomPerfect can handle that) if your mains are substantial and your sub very well behaved. That is the Geddes approach. Regardless, the processing required to integrate the subs or sub generally requires a line-level signal.