Amp for LS50

I had my LS50s running off my Ayre VX-5/20 while I was awaiting my new floorstanders to be shipped.  I was amazed at how well they performed with high quality power.  I have attempted to find a less powerful amp to run them in a second system and realize after some trials they really shine with quality watts.  You may want to acquire the amp upgrade first and enjoy what the LS50s can do while you are awaiting your speaker upgrade.

Good quality amplification (not necessarily big power output) will make your LS50 perform optimally. The LS50 need good quality amplification and upstream electronics, as somebody has already suggested here, in order to hear what these speakers are capable of.

I heard these KEF LS50 paired with the Naim Uniti Nova (streamer/DAC/integrated amp), which is an all-in-one box solution, and they sounded fabulous together very musical very fluid solid punchy and had excellent musical drive or rhtymic drive. The Naim Uniti Nova is rated at only 80 wpc @ 8 ohms and its power amplifier section uses class AB design. 
The Naim Uniti Nova has a very good digital streamer/DAC as well as integrated amp sections. 

However, the Rotel RA-1592 integrated amp and the Musical Fidelity M6Si integrated will also make your LS50 to sing. But as you upgrade your amp and upstream electronics the better they will sound or perform. Unlike other speakers within their price range (sub $2k/pair bookshelf speakers) these KEF LS50 would have to be fed by quality electronics in order to perform and sound good.

If you are seriously considering musical fidelity, check out upscaleaudio.com. He has the m2si integrated at 40% off the 1k msrp. Unless you go used and get more for your $$$. And can stretch it a bit, this Hegel here on AUDIOGON would have plenty of power for your ls50s 

https://www.audiogon.com/listings/lis98g51-hegel-h-160-h160-h-160-integrated-amplifier-solid-state

I agree with the other poster, $1000 is not enough to drive LS50’s. You may need to go up to $2-3k to be honest.

But if you can’t, then perhaps the NAD receivers or Outlaw Audio RR receiver is a good buy. Peachtree is good too, focus on integrated amps with less features. Two channel, don’t get some 5.1 channel home theater receiver with 10 million inputs.

What sort of sound signature are you looking for?
Actually, all amps sound great with the LS50 and while a better amp does make it sound a little bit better, I found my sweet spot to be the Schiit Ragnarok and anything after that is really minimal. A very good amp within your budget is the Cambridge CXA80, it's not as clean and revealing as the Schiit, but it comes with a decent DAC and is quite satisfying. I personally do not find the Musical Fidelity M5si a good match as it becomes too sibilant/brillant/harsh for me, but you may have higher tolerance. 
Also, save some money for a good DAC, I find it affects the sound much more than the amp, especially for the LS50.