Your sub experience: Easy or hard?

Trying to integrate one was very difficult. Never blended right and never sounded balanced to me. But integrating two was much easier and sounded great. I settled on line-level with a cable from amp speaker taps to a powered subwoofer for each of the two channels. 

I've run REL s/510 SHO with focal Sopra 2, Harbeth 30.2 and Harbeth SHLs 5 with generally good results in a purpose built room about 13x22. I then changed to a JL 113v2 and the JL crossover, CR-1 and now run this with Wilson Sabrina, crossed over at 60 hz. This set up is the best so far, very seamless integration due to both the JL's auto DSP room tuning and the flexibility of the CR1. I also use GIK room treatment and bass absorbers. The bass is subtle and tuneful, no boom. Roon also provides another means of EQ on the fly btw. I think most times subs get set to be too loud and then can border on being perceived as boomy. 

I've been using my Hsu sub for more than 20 years. I stick it in the corner and don' t turn it up too loud. It ain't that hard. 

One Rythmik F12G in between Maggie MMGs.  I recently added a small Miller & Kreisel K-9 in the corner opposite the Rythmik just to flesh out the sound throughout the room (it has one side open to the kitchen/dining room).   Only adjustment was to the phase control - it now melds very nicely with the entire system and is literally two feet from my listening position.  I get no localization from it. 

So..............neither sub was hard to integrate. 

Since I use a sub for "bass fill" to obtain full range sound in a good room, not difficult. I suppose if one is a home theater fan and going for dramatic effects it would be much more difficult. I have a two channel system, so I can pretty much set it and forget it.