Subwoofers - crazy upgrade!

SVS sells isolation feet that bolt right on to their subs, I have them on all my SVS subs and on a pair of Klipsch LaScala speakers. Well worth the money in my view. As others have pointed out... if one sub suits your fancy try two. When I added subs 20 years ago my love of music harkened back to my teens and twenties. It was like starting all over again. The CD by Herbie Hancock / Dis Is Da Drum took on a whole different meaning to me. As has much music. Once again, the adage "it's never too late" rings true.

I’m still using my circa 1999 Velodyne SPL1000 10” sub. Never tried another sub or a 2nd unit. Probably my loss.

If you stack subs, doesn’t that introduce vibration

into each sub, causing distortions?

This is a little excessive but it gives you something to dream about when you’re talking about stacking subs. https://share.google/PGq3mBI8pqe3sAbXq. 
 Now that you have discovered bass. Don’t overlook the need for room treatments, it too can be just as transformative. Good luck 🍀 in your stacking journey!

@ervikingo  Not friendly to my back.  My speakers go really low (REW shows them starting to drop at 15Hz) but I do have 2 subs on standby!

If your using -6dB rated sub-bass woofers read no further.

If your sub/s are rated at -3dB@xxHz, when placed on a small harbor frieght dolly using an inexpensively long interconnect from Blue Jeans or Monoprice Cable one can easily be rolled over to your listening position.

Repeatedly playing a downloaded low frequency cadence (not music) while slowly strolling around your rooms perimeter you should be able to easily locate and map your rooms standing waves locations where each sub can be positioned for their optimum presentation using the least amount of gain and EQ. 

When -3dB subs or and full range speakers are located out in most rooms null areas no amount of amplifier power or rated ability can overcome the physicality drain on the low frequencies by the null position.

This out of positioning has been the ongoing issue nurtured by either the manufactures lack of knowledge or a marketing stratagy towards the unique home audio market. 

PS: To reduce enoying low frequency born throughout your dwelling leave them on dence foam topped dollies. Take care of that back. Enjoy.