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
JL Audio makes a great sub.  In reality the sub rally changes the mid-range and not for adding bass.  You have to find the bass node in your room to find the best placement.  Audio Physic website has good information on setting up speakers.
You have to find the bass node in your room to find the best placement.
If a sub is fully controllable and there is a prime listening position, there are many possible placement sites. For stand mounted speakers slightly ahead of the main woofer to obtain the same driver / ear path length and minimal control affectation.

As far as placing the sub in the listening position and finding the spot with the most bass, I have never got it to work, even by crawling around on my knees to find the spot at ear level.
Yes, I have done just that.  But I had Magnapan speakers at the time.  It was wonderful.  The music exploded!. I currently have full range speakers now, no need for a sub.  That said if you beside to get a sub, check out "REL".
A sound system that wants great power efficiency will definitely require you to use a subwoofer. Subwoofer has many good types, such as: JBL 728S, Martin S218, EKX118, BMB, Bose ....
Refer to the subwoofer product at http://bit.ly/2SjOdMZ