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

Thx Jl35. I kinda had a feeling that it could help with a fuller sound. I’ll keep my eyes open for some good deals around Oakland. 

Modifiers by trying to boost the base could be resolved in two ways in my opinion:

1.  An equalizer
2   Instead of gimmicks and added components, if you could afford it (good used ones are out 
     there) 
     the Klipschorn or LaScala speakers would give you all the base without subwoofers.  Read      specs on these famous speakers.  I was turned onto them by a friend and co-worker 
     Tomlinson Holman, inventor of THX and creative director at Skywalker Ranch.  The 
      LaScalas were his studio monitors.  

Has anyone tested the Dynaudio Sub 3 or 6?For just extending the lower frequencies on a 2 channel system they look viable.

Just to share my experience:  in my large L-shaped room, my GoldenEar Triton 7's were just not providing the depth/weight of sound I wanted.  After doing a lot of research on upgrading the T7's and not coming to any conclusions, a pair of discounted subs caught my eye (SVS SB12-NSD subs, substantially discounted at $400 each, as other have mentioned here).  Knowing that SVS allows free returns, I purchased a pair, just to see if subs would help give the bigger sound I was looking for.  For me, with one placed next to each Triton 7, they definitely do, and I now consider the $800 I spent on them to be pretty much as worthwhile as the ~$5K I've spent on the rest of my setup (T7's, GoldenEar center channel, Marantz preamp, Emotiva power amp, single 15" Hsu sub).

I don't have the knowledge/experience to offer any suggestions on sub comparisons or placement, but to me, these two entry-level subs made a very large difference that my single 15" Hsu, perhaps because of positioning, had not.