That is a good size room. I would definitely recommend against Bookshelf/Standmounts for that purpose.
Philharmonic Audio BMR Towers
JBL Synthesis HDI3800
Monitor Audio Silver 500
Paradigm Founder 100F
Polk Legend L600
If you are mostly into Music... get the best quality neutral Speaker you can. I'm an avowed fanboy of Philharmionic Audio, and the new BMR Tower is seriously legit. My mains utilize the same woofer (8" Revelator) and my Center and Surrounds use the same Mid and Tweeter (BMR Driver and Raal 64-10, respectively). For a center channel you can get a single BMR Monitor: it will blend perfectly well.
I'm not a big fan of KEF. They do sound good, but caused me some fatigue. (Purely personal... many others don't have that problem, but for the cost you pay on the R Series, you can do better.)