Oh boy, I sure would like to hear those Kanta 3’s. Extending their bass, for music sometimes? For video sometimes? Complicated!!!
My advice: Stereo Pair of Subs located with the mains to maintain imaging. Careful control of crossover and volume. Self-powered, independent of the video system, i.e. extended bass ALWAYS.
As you must already know with your speakers, low bass is more directional than many think, and it has been pointed out, the narrower overtones of the wide low bass fundamentals give directional cues to the fundamental’s location.
......................................
The better the mains, the harder it is to achieve seamless extension, and you probably cannot personally listen, likely buy un-heard, I would want full return/refund (not store credit).
....................................
If ONLY for Video, adding bass effects i.e. Dinosaur Stomps, a single self-powered sub will work, balanced to be unaware of location or contribution unless you turn it off. But ....
When via 5.1, using sub out, then when using ’direct’ which is often 2 channel, or 2 channel mode, often the content’s original format, the sub will be off, no extra bass. I very often find the cable company or my AVR send/invent/use surround without me choosing it, and 2 channel sounds better. Therefore, for ANY home theater, you still need a decent amount of bass from your mains.
For stereo music or stereo video, extended bass always, a stereo pair of subs is needed, and very carefully chosen and controlled crossover/volume to work seamlessly with your existing mains. They need to be self-powered to maintain independence from AVR system.
..............................................
I suggest you further arm yourself for evaluation.
piano lows, bass, drums: I prefer using stand-up bass to evaluate bass: quality, control, directionality.
scroll down to chart of frequencies
https://www.studybass.com/gear/bass-tone-and-eq/bass-frequency-range/ unique double bass album
https://www.discogs.com/Niels-Henning-%C3%98rsted-Pedersen-Sam-Jones-Double-Bass/release/1703343 mingus dynasty, two bass players, opposite channels in 7 piece band
https://www.discogs.com/Mingus-Dynasty-Live-At-Montreux/release/1448034 Duets, alto sax and upright bass only.
https://www.discogs.com/Lee-Konitz-Red-Mitchell-I-Concentrate-On-You-A-Tribute-To-Cole-Porter/release/2436055 aside from wonderful music, the full range and textures of Red Mitchell’s bass are there for every track, and a long bass solo on the last 9 minute track, incredible. No masking of drums, guitars ...
...............................
my music system: horns with 15" woofers, no sub
my video system, single self-powered sub, via 5.1, mains have 10" woofers for bass without sub, sub far from mains
my office system, bookshelf with single self powered sub, always in. music and video from 27" monitor/pc
...........................
good luck extending those beauties. btw, manufacturer probably has some advice, perhaps knows what other owners have tried/done.
Elliott