Best Integrated Amp (for me)

Out of the box- Musical Fidelity a3.2 integrated amp.  110wpc with an excellent phono stage.  Dual mono construction, and excellent sound.  Built to last another 20yrs.

Marantz has several very well regarded integrated amps that would be within your price range.

I currently have the Acurus DIA100 mkI partnered with Monitor Audio R700MD’s and I completely disagree with those above who said the mkII is bright.  The mkI, or at least my mkI, is in no way bright sounding at all, (although, I have read that sounding bright is the knock on some of these DIA’s).  
Mine is very beefy, sweet, and transparent sounding and I may be looking to sell it as I am moving overseas in a few months.  I am considering a smaller shoe-boxed size integrated.

I recently bought a Willsenton R8 integrated from China after it received very solid reviews. All hand wired KT88 integrated. I’m very happy. It’s my second KT88 integrated. I’m acquiring a collection. Great $1000 investment. 
https://m.youtube.com/watch?v=U0BDFT4f55w

As the owner of two pair of LS 50s, I can tell you that they definitely benefit from serious amplification. The Rogue Sphinx suggestion seems like a good one to me.

Consider a used Bryston B60.  It drives my LS50 fine.