Amp for LS50

Get the Rotel RA-1592 stereo integrated amp ($2500 new) it has built-in DAC.
Also consider the Musical Fidelity M5si I integrated amp ($2k ish new) or the M6si integrated amp for $3k new.
These will pair really well with the KEF LS50.

I am using the Peachtree Nova 150 at the moment. It is very good and fatigue free. I could get better amplification but I do not think it is warranted with the LS50. I will be buying a new set of speaker soon, KEF Reference 1 or Magico A3 and for that better amplification makes more sense to me.

I am also going to upgrade my Nova 150 to the Nova 500 in Spring 2019. The Nova 500 has a different preamp section than the 150 and 300. I will likely drive the LS50 with the Nova 500. Overkill for sure but the price of entry is rather low.

I have the Class D CDA 250 and like it a lot.  I have owned it for about a year.  I can listen for hours, as it is not a fatiguing listen at all.  

Admittedly, I do not know which type of modules it uses (ice power, etc), which seems to be important to know in any discussion about D type amplifiers, in general. 

I am not sure how the Class D audio will pair with the KEF LS 50s though.

I am finding that the CDA 250 sounds better with some of my speakers than with others.  The other amp in rotation is the tube Prima Luna Prologue 5, which I have had for 13 years now.

I am finding that the CDA 250 sounds better with the traditional 2 driver speakers I own (Opera, Wharfedale), whereas the Prima Luna sounds better with the single driver systems that I like (Omega).

Rich 

Your KEFs will respond well to a LOT of power. I have R500s in my second system powered by a Mivera amp with an IcePower AS1200 module and 700 watts/8 ohms per channel works very well. One of the amps from Apollon or Nord using IcePower or Hypex amps would be a good alternative if you wish to go class D at the budget you mention. As the LS50s are quite revealing, any increases in preamp quality and transparency you can afford will be rewarded.