Best sub for music,

Svs has been a front runner lately there 3000 Sb, and 3000 mini 
are very good ,and many awards on the 3000 sb
and very high tech most others subs do not have such as a dual range Pole piece,at low volumes tuneful using the inside ,when music is turned up the whole pole piece is used ,and 50 bit processors very high current mosfets on the outputs and one thing 
most others don’t have a excellent app to control  many functions on demand.

Velodyne servo subwoofer 

Don’t overlook Rythmik.  These are very good sounding and well made powered subs for music.
https://www.rythmikaudio.com/F12SE.html

I do not know where this differentiation between home theater subwoofers and HiFi subwoofers came from. There are good subwoofers and bad subwoofers. Perhaps home theater people tend to buy bad subwoofers. Good subwoofers will do anything. They are even better at doing theater than bad subwoofers. 

Most commercial subwoofers are not even fit for home theater duty. It is very hard to make an enclosure that works at a reasonable price not to mention terrible cross over strategies. Play anything with a lot of bass and put your hand on your subwoofer. That vibration and shaking is distortion. Ideally you should be able to put your hand on it and feel absolutely nothing. I made 200 lb enclosures out of solid surface material and I could still feel some vibration. Next versions will be better.
Stay away from ported subwoofers. Subwoofers have to move a lot of air and it is very hard to avoid port noise. It is better to stick with sealed designs and correct the frequency response with power and room control.
The best subwoofers now use what is called a balanced force design. Two identical drivers are placed at opposite ends of the enclosure and operate in phase so the vibrational forces cancel out.
 Regardless of the size of the room the minimum size is two 12" drivers or four 10" drivers. Bigger and more is always better. The less work any single driver has to do the lower will be the distortion. Making sub bass requires long excursions which take the suspension out of it's linear operating range. Bigger and multiple drivers do not have to move as far. The thought that smaller drivers are "faster" is beyond silly, another example of lay instinct run amok. The sign of a driver not being "fast enough" is it's high frequency response falling off. Any subwoofer driver that can make it to 500 Hz is more than fast enough. I do not know of a subwoofer driver that can't make it to 500 Hz. There are lots of great drivers out there. It is the enclosures that are the main problem followed by poor integration strategies and crossovers. Digital bass management and room control are essential to achieve the best results. 

The best sub for music isn’t a sub but a bass extension. Genelec W371a with GLM digital management. Bargain at $19K a pair.

https://www.genelec.com/w371a