@awooof --
What are your main speakers?
I take it there are quite many ways to achieve well integrated bass augmentation, some of which have been mentioned here already, but be prepared to invest time, effort and patience to wring out the fuller potential integrating sub(s) with your fronts and acoustics. REL subs are popular and very well regarded as music subs in particular (a notable advocate of REL's is Paul McGowan of PS Audio - see his youtube videos to learn more on subs use and integration). JL Audio subs seem to bridge music and Home Theater prowess by being somewhat more powerful than REL's, and I'm not sure how their prices compare to REL, but they're not cheap. Then there's Funk Audio subs, which are also expensive and by all accounts they're extremely musical as well as being immensely powerful, using mostly 18-24" units in sealed, beautifully crafted (plywood) enclosures. Seaton Sound seems to provide great "bang for the buck," as do Power Sound Audio, HSU, JTR and others. Audiokineses Swarm multiple-approach subs are very interesting. SVS makes very good subs as well and also need mention - I've used a single SVS SB16-Ultra in my setup; a versatile, very high quality sub for both music and movies, easily providing the floor-shuddering effect (with immense power and weight) that comes from <20Hz performance while being subtle, informative and relatively "invisible" when needed. A great overall performer, which I intended to eventually use in pairs with another SB16-Ultra, but ended up going the horn subs route instead to augment my all-horn main speakers (more on that later).
You do in particular specify "elite subwoofers." Well, to me there's no divide or dichotomy between "subtlety, finesse and musicality" - the usual go-to goals among audiophiles - and sheer, visceral power (rarely the traits sought by audiophiles); to the contrary, and both are needed to go "all the way," if you would. Headroom, and lot's of it, work wonders in the pursuit of a smooth, effortless and present/informative sounding bass, as do large radiation area, and as a general rule therefore I'd go with the bigger-driver subs, in pairs or more. Overkill to some; sorely needed headroom in my view. How one seeks to attain this goal though is not trivial, and calls for careful consideration in light of one's needs and practical, interior layout and limitations.
Going further with the need for headroom my search has led me to DIY enclosure designs that do the heavy lifting, increase sensitivity, and relieves the driver - namely tapped horns (Danley Sound Labs holds the patent for TH's, but endorse DIY community efforts to build their own iterations). Depending on their LF-capabilities the upper range bandwidth of TH's is limited (usually not a problem with audiophiles that tend to cross over rather low), and they get quite big indeed, certainly if fairly flat <25Hz performance is required (Front Loaded Horns get even bigger). However, with the proper design, driver and build quality tapped horns puts out massive quantities of bass, but first and foremost the bass quality is excellent - something very few in the audiophile community seem to be aware of. Compared to the SVS SB16-Ultra I used previously my new pair of tapped horns, even far from being run-in and properly implemented, exhibit no audible smear, have a fuller and more natural midbass, and are smoother, even liquid sounding with a tactile presence that expose detail and information in the bass I've never been aware of. Not least: they integrate noticeably better with my all-horn mains.
Many ways to skin your cat, as they say, but I find you shouldn't skimp on size, sensitivity and overall power handling to get the whole sonic picture - re: elite sub performance. Good sub(s) hunt..
