What are the best subwoofers you have heard for music. Speed, Musicality and integration

ATC C1 MK2 subwoofer : choice of real wood veneer cabinets, premium hand-built drivers, and ATC’s standard 6 year warranty. Highly recommended.

Best of breed in the up to $4K strata, that I auditioned (and bought) to complement my HARBETH speakers.

https://www.theabsolutesound.com/articles/atc-loudspeaker-technology-launches-c1-sub-mk2-active-subwoofer/

https://www.whathifi.com/news/atc-launches-compact-c1-sub-mk2-active-subwoofer