Kef LS50s - great like me but need to come up for air

Seeing as you love the LS50s, you could try

• Feed the KEFs with a tube amp
• Try a tube preamp-e.g, Schitt Freya Tube Preamp, removing the NAD (under your budget)
• Add a high quality, musical subwoofer

Each of these has some big benefits and would result a potential meaningful change without ditching the KEFs.  

If you want to replace the KEFs, there are great example suggestions above.  I loved the LS50s, but I preferred the Wharfedale Linton Heritage more--yet it is undisputed the KEFs had more detail and were a more advanced design.  The Wharfedale are super musical and smooth.  

I love the suggestion on Heresy.  If you could swing it a used Forte III (likely in the $2K range, they would sound super in that room size and you might not ever want a sub.  Heresy IVs are supposed to be spectacular.  I haven't heard those.  Disclaimer:   I moved into sampling and keeping horns about 3-4 years ago.  So I like them.  The power and clarity (AT LOW VOLUMES) with that Schitt into a Heresy or Forte would show you a relaxed big audio picture.  They are so efficient that things should open up to your ear.  

Enjoy your journey!  You are in a fun spot.  My recommendation is to have some fun if you have the time and patience.  

Sometimes we just need to try things out for ourselves.  It can be super fun, but also stressful so keep us posted!

I've heard the Epos, the Dynaudio, the Harbeth 3/5 and Usher.

My vote actually goes to ProAc Response 1 speakers.  If floorstand is OK, perhaps an audition of the PMC twenty5.23, not a big floorstander and the sound quality is really nice.

If budget allows, I can recommend the Sonus Faber Electa Amator bookshelf with a matching Sonus Faber sub.

Let us know what you have decided later.  :-)

How about the new KLH 5 recently reviewed by Stereophile? I think they're $2000 for the pair, not too big & if they are basically a modern version of the classic KLH/ AR / Advent sound, might be just what you want. Smooth, laid back w/ excellent bass. IMO, acoustic suspension bass design, if properly done, can yield the most realistic, tight, clean & extended response of all designs especially now w/ modern drivers & crossover components. Lack of efficiency is their only issue. Some very expensive speakers today utilize it, new Magico's, YG Acoustics etc. KLH is also coming out w/ a smaller, two way version, very soon. 

+1 

try a nice tube amp with the kefs

in a small room like yours you don't need alot of power, shouldn't break the bank

otherwise spendors, proacs and harbeths would bring some nice warmth and luxurious tone without excessive detail/stridency

Let me suggest a totally different solution.   I assume you have a sub to go with the LS50 pair, and if you don't, you should.   Get a miniDSP DDRC24 active crossover with DSP EQ built-in and the accompanying UMK-1 measurement microphone.  Use it to balance between your LS50 mains and the sub.   Measure the system in that room, then create a desired system response and program the miniDSP to do that for you.  

The LS50 is a very fine loudspeaker, especially at the price point you're working at.