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

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!

I added two REL t9/i subs to my 2-channel.  Being somewhat of a dumb 2-channel purist and wanting to keep everything planar I was resistant to add the subs. 

Ive finally come to accept that I now have separate subs in the room and the sound is fantastic.  Just the right amount of room pressurization allowing for excellent slam in upper base and extension in lower frequencies.

I can try just powering a single sub to see how it compares and get back to you 

Subwoofing for 40 years now,biamp and also use an electronic crossover.....i got 5 sub woofers some big 15"some not so big10"they can really help out a system.I remember when I had KEF 101s and a subwooker ..would blow peoples mind how much music came from the KEFs,LOL,later on I showed them why ...a big subwoofer hidden away....

I wanted to post a shot of my IDEA Sub connected directly from my PassLabs XA25 amp in parallel with my PMC Twenty26 using Western Electric speaker shielded cables by TimePortal. Anyway the package of one sub and PMC sound wonderful. I couldn’t believe the results. The PMC stopped chuffing and the bass balanced beautifully. Using the sub crossover and level allows to customize to meet track needs. I’ve never looked back. Thought of trying other subs. This one is a 10” active and passive dual design. Works a treat. My bottom line? Experiment.

Ive had a set of Magnaplanars in a room of similar size to yours, and have always found large, slow 'subwoofers'i.e. Velodyne, JBL, etc just result in muddy, discontinuous sound. Not expecting very much, I tried a Martin-Logan Dynamo 300 8" powered sub and found it filled in the bottom end seamlessly. It has been superceded by the Dynamo 400 , an excellent product and an excellent value.