Are big subwoofers viable for 2 channel music?

@smodtactical , For that space you are going to need at least two 12" subs with excursions over a cm or you will be pissing into a forest fire. 

The idea that music requires different subwoofers than theater I find very odd. Any sub system that can reproduce down to 18 Hz accurately is perfectly acceptable for both. 

What is speed when it comes to driver performance? What does "faster" mean? The faster a driver can move the higher the frequency it can reproduce. If a driver can move fast enough to reproduce 500 Hz then 100 Hz should not be a problem at all. What everybody is referring to when they say "fast" or "faster" is transient response. The diameter of a driver is only one factor that can influence transient response. There is also the stiffness of the suspension, the weight of the moving system, and the power of the drive motor. The point is, when it comes to reproduction under 100 Hz an q18" driver is no slower than an 8" driver. Anyone who thinks so is just falling prey to "lay intuition," 

There are many excellent subwoofer drivers available today. The driver is usually not the source of problems. It is that enclosure that separates the men from the boys. 

When it comes to big vs little subs and one vs many, I don't care.  I just want the best performance for the money.  I already have a Velodyne dd18, Infinity Intermezzo 1.2, and the tiny PSB.  One thing that I know is that it's impossible to get flat bass in any room I've ever been in with a single sub and without a lot of bass traps and eq.  I tried when I was in my twenties and it's not worth the trouble.  I did get really flat bass with the help of 25+ bass traps and extreme eq.  It sounded weird, though, and I didn't stick with it.  I find the claim that multiple subs can solve a lot of room problems plausible.  The more you have the less hard they all have to work and I'm confident the room nulls can be solved by this.  Since the more you have the lower volume setting they'll all have, the node excitement is bound to be reduced.  The main problem with small subs IMO is that the small driver needs extreme excursion which means extreme pressure in the box and a ton of power.  These things are very bad for longevity.  

I'm not opposed to having 10 18" high sensitivity subs but if I can avoid it I will.  I agree that high sensitivity has a sound characteristic that I like.  

I can confirm that the Snap AV sub is a good quality littlle sub.  It's got good output down to 37hz, pretty much done by 30hz.  For an 8" sub for $112 on ebay it's a steal.  Gloss black box, good controls,  I wonder if all custom install only brands have terrible resale value.

JBL SUB18. Peak output of 137db and gets pretty low while doing it, Pretty nuts.

https://jblpro.com/products/sub18

https://www.bhphotovideo.com/c/product/1221512-REG/jbl_sub18_high_output_studio_subwoofer.html

["jon_5912       I already have a Velodyne dd18,    One thing that I know is that it's impossible to get flat bass in any room I've ever been in with a single sub and without a lot of bass traps and eq."] 

I suggest using the TIP: on page 23 in the Velodyne DD User's Manual or running the Sweep Tones while walking (Crawl Test) your room and mapping the the loudest bass modes for a potential sub position. 

If your DD-18 is positioned in your rooms loudest bass mode resulting from the TIP or Crawl Test with the mic at the listening position you should see a reasonably improved before and after result after running the Self EQ.

The initial goal is a relitivly even (not ruler flat) frequency response from the speakers 200Hz and the subs frequency adjustments beginning at 100Hz to where your speakers just begin to fall off. These are your crossover region adjustments which should be saved to your presets. Everything below that frequency are personal taste levels.  

Unfortunately the manual LOW PASS, SUBSONIC, CONTOUR frequencies / slopes, PHASE and POLARITY parameter adjustments can be a tedious task using the sweep tones and confirmed with some music, also stored to memory.

Despite its twenty year old software these efforts will result in greater adjustability and detail compared to most any current onboard subwoofer processing today. Hardly impossible.

DD Plus does it all along with added discrete Q filter building automatically leaving some quick multiple drag and drop Manual matter of taste adjustments.