Your sub experience: Easy or hard?

It wasn't hard at all, it was fun. I enjoyed the "subwoofer crawl",messing with the crossovers, plugging and unplugging ports.I have two HSUs and one SVS.If the HSUs ever stop working I would have all SVS.Controlling all of settings from the listening chair is wonderful.

I have two REL S/812.  The reason for two is mono block amps.  I found the setup to be quite easy and once dialied in, the improved sound is well worth it.  The only issue I have is playing the occational disk/LP that is very heavy in the low-end bass.  Then the subs are just a little too present.  But overall, they are spot on the majority of the time, and if I have to turn them down a click or two at times it no big deal.  

I have a pair of Sopra 3s that I tried to integrate with a pair of REL s/812s. I tried for months to get them to sound acceptable in my room, even broke out the REW software. But no matter what I did those RELs wouldn't integrate well enough.

Someone proposed the idea that I didn't have enough control over the RELs and that they wouldn't necessarily go deep enough anyway. They said try to audition a pair of Rythmik f12s instead because of the number of controls on their back plate.

Well after a few months I did manage to get a pair and I found them extremely easy to integrate into my stereo system. And it only took me a few days in total to get it right. I then gave back the Rythmik f12s, sold off my REL S812s and bought a pair of Rythmik G22's. 

Couldn't be happier... Although I'm thinking about buying one more pair of them.

It depends what you are trying to do / solve with subs.  I have an extremely difficult problem so the solution, including using 2 subs was also difficult. The problem could not be solved without subs as placement was critical, simply buying a pair of speakers or amp with more bass only made the problem worse. 

In the early ’90’s, I tried like heck to integrate a sub into my two-channel music system. All the subs I dragged home just didn’t integrate well since they were all essentially home theater subs that were non powered with passive internal low pass crossovers. It just didn’t work and I gave up. All of the cabinets were either band pass cabinets with just a port exiting the box or a typical down firing, ported cabinet. There seemed to be no such thing as an audiophile subwoofer back in the early ’90’s other than maybe some JBL models which were not obtainable to a broke kid right out of college.

Fast forward to 2020 when I started planning a completely new 2 channel system and with nearly 30 years of more experience (especially in the pro audio area), integration of a pair of 18’s was very easy. All passive speakers with outboard electronic x-over made it easy. Also, a much better budget certainly helps!

My 2nd system in another room is also using a pair of 12" low frequency drivers in sealed cabinets supplementing 8 inch two way stand mount speakers. Again, passive sub cabinets crossed over by an outboard Sumo crossover into dedicated subwoofer amplifier and dedicated mid-hi amp. It’s easy when you’ve done it a few times and know about how things should be initially set up (crossover point & slope, gain structure, etc.). Tweek a few things with the ears and one is good to go.