Speakers for 2nd System!

If you plan to listen at low volume levels, high sensitivity speakers make sense but the trade-off is that it's very difficult to get low bass out of a high sensitivity speaker. Not impossible, but a real challenge to the designer. This is one reason why people with these types of speakers utilize subwoofers. Finding a speaker that is aesthetically pleasing, sensitive, has a small footprint and decent bass could be a problem. Good luck!

Here ya go, outstanding and can be bi amped.

https://tmraudio.com/speakers/bookshelf-speakers-monitors/legacy-calibre-xd-active-bookshelf-speakers-rosewood-pair-w-grilles-open-box/

@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..