And what about a RS212 paired with the OB110?
Personally, I can't see myself doing that.
I think a lot of this has to do with how we individually look at things.
I currently have two RS212s. For a time, I had two RS210s and had kept one. I sold it not too long ago because I didn't find myself using it for much other than a very cool looking stand for my RH450 for headphone practice.
If I had an OB-110, I'm sure I'd only use it by itself, when/where that was appropriate. If I needed or wanted more, I'd go to an RS212. If I wanted more than one RS212, I'd grab the second RS212.