Has anyone added a small subwoofer to 2 channel and been thrilled with the result?


The subwoofer can of worms.
I’d like to add some bass to my otherwise fine 2 speaker setup and have limited space so perhaps a single 10in?
After a few weeks of research the only conclusion I can come up with is - everyone agrees they have to be setup properly. Every brand and technology has their own following and most recommend using 2 (which I don’t want due to space concerns). My room is 12 x 13 ft with box raised ceiling.
After much research, these are the subwoofers I’m trying to pick from, for various reasons:
Rythmik FM8  - lots of hifi fans
JL audio e110 - fantastic support
REL T/9i - sort of a gold standard
KEF R400b - interesting technology, makes me grin. 

I've never heard any of these.
System:
Hegel H160
SF Concerto speakers on stands.
Ben
casteeb
Post removed 
All of my systems include a subwoofer (or two or three or...).

I have a couple off small computer systems in smaller rooms and use small sealed subs in both, a Rythmik F12 in one and a SVS SB12-NSD in the other. I love Rythmik subs and think they are hard to beat for the money, but SVS is no slouch either. The SB12-NSD is an incredible bargain right now. They have been discontinued and heavily discounted. You should add that to your list. 
It's remarkable what a sub can do for mids and highs...I use a REL S/5 SHO, but have had great success in past with small REL in small room system...
A number of the Rythmik plate amps (all but the XLR models) provide both high-level connections (on speaker binding posts) AND line-level connections (on RCA jacks). You can try the sub both ways, and use the method you prefer.