Speakers for 2nd System!

@lalitk --

I know the Leben quite well (also the smaller sibling, the CS300), and it’s a fine amp. I might try and look for a used pair of WLM Diva’s (the floor standing model as an outset), which are very good speakers built around a 10" coaxial driver with a stated 97dB sensitivity. At the time I heard them over the Almarro 318B amp, a lovely pairing, and my guess is the Diva’s will mate well the CS600X. Being a single point source per channel you’ll also be able to sit fairly close to the speakers and still have excellent summation. To boot: with their slender and finely veneered shape they're nice on the eyes, I find. 

Compact and efficient are pretty much mutually exclusive.  The closest thing that comes to mind would be an offering from Omega:

https://omegaloudspeakers.com/collections

Your amp has more than enough power for a more typical 90-91dB speaker in that size space which would open up your options considerably.  Unless, you need to listen at 95+dB levels, you should be fine with a more realistically spec'd speaker. 

He forgot to mention " The speaker should also make me soup & sandwiches" on his want list.

your going to have a VERY hard time finding everything on your want list..

This is a great project. Look at the Devore oBaby, above Audio Note, you can chase those way over budget if you want, Fyne makes a small speaker but not sure of the power needed. Good luck and please keep us in the loop as you put this together.

Good recommendations so far, keep ‘em coming! 

Omega and Horning are on top of my list. 

I do not want speakers in 86-90dB range cause I have plans to rotate SET (2W-8W) amp / pre combo down the road.