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

Have you heard Buchardt? The S300's are about $1400.

I have LS-50s as my primary speakers. the 'body-hugging Ferrari sports seat' analogy is not far off. If your room placement can accommodate them, the Magnepan .7 is everything you are asking for. and will not leave you feel like you have compromised. With lesser box speakers than the LS-50 (and that's most all of them) you will rapidly become annoyed with box colorations that simply don't exist with the LS-50 or the Maggie .7s. The .7s, on the other hand, will provide you a transparent and large window that is a very different, but equally enjoyable, listening experience. 

If your NAD amp will drive the LS-50s to your satisfaction, it will handle the ,7s as well. 

My second recommendation, only if placement limitations preclude using the Maggies, would be the KEF R3. Think of that as the luxury GT version of the uncompromised sports car that is the LS-50. A little bigger, a little softer, but definitely cut from the same cloth. And in this case with another 1/2 octave or so of quite noticeable bass. A warmer, more forgiving speaker than the LS-50, for sure.

And I have to laugh at the Heresy recommendation. The most gawdawful speaker I've ever heard, No low bass, squawky,honky mids and harsh tweeters. Yes, they are efficient, and yes a good tube amp can tame them to some extent. I've always wanted to like them for their dynamics, but in 50 years of listening to several versions of them, on all kinds of amps, SS and tube, I've never heard them sound even good. The only Klipschs I've heard sound good sound were far bigger and in a very large room.  That seemst to be their place.

Magnepan LRS

you definitely do NOT EVER want to put vandersteen anythings in any room that small, 11 x 14 is way too small for those speakers to sound as their designer intended, you will hear shoutiness at the crossover point @ 2.8 kilocycles. i learned this the hard way. those speakers are meant for a substantially larger room, like twice the size, at which point the shoutiness goes away and the magical imaging [with real depth] happens. a speaker i've used for many years now, the thiel cs.5, OTOH works very well in that size [11 x 14] of listening room, and unlike their bigger thiel brothers, these speakers are mellow yet still reveal details in the treble range that lesser speakers [including the aforementioned vandys] gloss over.

Hello,

I like all of the ideas above. I am wondering if you can accomplish your goal with some different speaker wire. I am going to suggest Straightwire speaker cables. 
specifically the Expessivo II or the bigger Expressivo Grande II. You will be amazed at what these cables can do for your system. You get to keep your setup but just change the cables. Just so you know when KEF is demoed at shows they use Straightwire cables. They go together perfectly. You can keep the speakers you live but change and probably improve the sound quite a bit. Plus, these cables are so universal you can put them on almost any speaker. If you are in the Chicagoland area this store I buy gear from is a KEF and Straightwire dealer. 
holmaudio.com

Also, you might want to look into the power cables. Straightwire has a Grey Lightning or Black Thunder power cable that won’t break the bank but really optimizes your gear. A different approach than changing from the LS50 to Harbeth speakers. I hope this helps.