Your sub experience: Easy or hard?

Easy. This system was easier the previous. Full range towers are way easier then standmounts. Just filling in the low low. I listen to lots of bass heavy music and the sub is a must. RTJ3 on vinyl as I write this. The sub disappears. Blends seamlessly and provides a more visceral experience at low listening levels. Took 30 minutes to find the correct placement and another few listening sessions to pin down the crossover and level. Easy peezy.

REL subwoofers are different.  Their high-level connection allows them to play more as woofers.  You also need to add a pair and at least start with their SHO series.  Then make sure not to play them with over a 40% volume and dial things in to make sure they blend in.  Bass fall off with volume and you will notice is you are able to play you system with lower volumes and still hear bass.

We can assemble the modules of the ISS built in different countries and assembled in space with success. We can have a “relationship” through AI. We can pinpoint and “paint” targets for invisible air strikes. 
Why in the heck can’t someone figure out an intelligent sub that can adjust volume as needed per recording?

Much easier with two than with only one, and also much more noticeable sonic improvement with two.  I would like to try three or four.

I have 2 rel s/510s. They’re magnificent but with better bass comes the need for battling room resonance. Also, the loudness of the bass from track to track can be all over the place. I wish I had remote volume controls on them.