Best sub for music,

I’ll probably get promptly booted out of here and banned for life for suggesting 18" JBL drivers on an audiophile forum

Nah. 18s are cool. The bigger cone needs less excursion. Very nice for extension in the bass. The only real issue is the size of the cabinet to work with one.

jheppe815, welcome. You are absolutely right. Having a system that really produces low end is a lot of fun and frequently brings on smiles and laughing. I have many recordings of large organs that are so much fun to play for people. Every time a 32 footer lights up your vision actually blurs!
You get some really funny reactions. But most importantly with good live recordings you can close your eyes and feel as if you are at the concert. It is every bit as audibly enjoyable as being at the event. If you just listen to solo female folk singers playing guitar then I suppose you can do without a subwoofer but for everything else? Let's put it this way, the people that have decent subwoofer systems are having a lot more fun:-)

jheppe815, I use QSC amps to drive my subwoofers. I am not familiar with the JBL amplifier but using an expensive high end amplifier on subwoofers is totally unnecessary. Commercial amps are much more fairly priced and there are many sound reinforcement amps that have excellent bass. 1000 class AB watts with a damping factor 500 or above and a big power supply will generally fit the bill perfectly.

I agree with poster jheppe815 on the JBL subs. I use two JBL B460 18'' subwoofers crossed over @ 50 Hz from the mains. It's eargasmic!

My approach with subs has always been "keep it simple".  I start with one and place it, walking the tightrope of performance vs permissible location. 

I throw on some bass heavy tracks and query A) Does it sound good? B) Can I locate the sub? If the answers are yes and no respectively, I leave it there. 

IMHO an unfortunate symptom of audiophilia is the need to endlessly complicate everything. 

I can’t add much more expertise than MC and Atmosphere, but only my personal experience. MC is correct that more subs even out the bass nodes. Atmosphere is correct that larger cones mean less movement and a smoother response. I have a small sealed REL for a small room that works well with my stand mount Von Schweikert VR-1s. I have two Hsu subs that work well for my music room with HT. The idea that you don’t need subs is folly. Music and its harmonics go below 20 Hz. That’s the goal. I think it’s better to go with two or more subs properly positioned (see the Harmon white papers) is better than the best single sub. I recommend setting your highest budget and starting with two subs of good quality, position them properly and tune them to your system. Reach for sub 20 Hz at a reasonable level and add subs when you can. One expensive sub is not better than two subs of lesser “quality” for the same price if properly positioned. It takes time and effort. Ideally you won’t even know the subs are there, until you turn them off. Best of luck. Play on!