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

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

No brainer - haven’t read the other posts just be careful.  Definitely go with two subs if possible and place each one as close to each bookshelf speaker as possible to minimize any timing issues.  Just go small - 8 inch driver.  Rythmik are great so are REL T Zero’s.

I have Raidho XT-1’s and I’ve paired them with B&W PV1D’s and I would put this system up against the best full range floorstanders on the market.

I can also use this to watch movies with outstanding results due to the improved bottom end.  I cross mine over rather high at 80hz at the advise of Raidho.  Call your speaker manufacturer to get tips.

Rob

I currently have a set of KEF LS50’s in a large room, 20’ x 24’ x 9’. They are on stands and I’ve used two different configurations. The first was a set of one cubic foot Klipsch 8” driver with two passives. The second sub sat directly on top of the first. I tuned them together andnthe sound was as a single sub. One coming in lower and the other tuned just a bit higher.
Great sound but I needed to thin my gear. Sold them quick and easy, still miss them. One cubic foot with 350 watts each was a very nice sub. They were 308’s

The second setupmwith the KEFs was with a 10” sun from Klipsch again. 
Side Note; I love the PSA subs I have for my main system but they are huge and multitask for HT.

the 10” sub does a very good job as well and is set up and being used as I type.
Have fun!