Kef

A little more information may be helpful here....

Yes they are.

The LS50 is good. But it needs power.

The R-series are good to on naim.

Hi,  Rega Planar 3 TT Bias 2 Cartridge.  NA CD5 player, NA CD5 integrated amp and Flatcap 2 Powere supply.  Through Rega Ela M2 speakers.

Everything is about 18 years old.

If you haven't already done so, the most important thing to do is to get the Nait 5, Flatcap and possibly the CD 5 serviced.

I have a pair of iQ3 and when I was in a transitory living situation I used them on my SN - sounded very good.  (Sounded much better than they now do in my second system powered by a NAD amp; amazing the difference almsot10 X the money can make!) 

Of course these are no longer produced and a good bit below the price point you have set.  But my Naim dealer does sell them.

You allready have very decent and good speakers

Kef will perform different not neccesary better

I'd look into max out your existing setup before putting money towards new speakers:

Rack

wall mount

new cart

cables

service

Well, I can't speak for all KEF's but I'm currently using a pair of LS50's while my BC1's are hors de combat.  And I'm loving them!  Considering the designs of the two speakers could hardly be more different I'm amazed to find that they have some surprisingly similar strengths.  In particular I would rate both speakers as amongst the most natural with female vocals I've heard at any price.  I have a feeling that the LS50's may particularly appreciate the current delivery of Naim amps.

I created a dedicated sound room a couple of years ago. I could not get my Naim speakers to work well in there, in any configuration. I owned Credos and nSATs at the time. I tried LS50s. They too didn't work well in the room. I traded up to Kef R700s. Bingo. I then added room treatment. More improvement. Since then, I have tried from time to time to see if I could get even more from my system from other brands of speakers. Recently I brought home a pair of Linn Majik Isobariks. They work even better than the Kefs in that room. In the end, it all comes down to how a given pair of speakers drives a room. There is no substitution for trial and error in your own home, with your own equipment. If you can't get a home demonstration, then buy used, if you can, and try them. If they don't work with your room and/or equipment, sell them. The Briks were almost half the price of new ones, and mint. Fantastic value buying used.

Tried LS50s here, no good for my room, very bloated bass (plugs didn't help) and sent them back. Much preferred R300, more neutral.

Recently tried R500 floorstanders and they sounded like loud party speakers to me, no nuance at all.

So I'm not so sure that KEF is such a natural fit for NAIM power, albeit in my experience of the above. 

What takes place in a service?.  Do I have to send everything back to Naim.    Although my stuff LOL is quite old I can honestly say it has not being played form more 300 hours.

I remember many years ago being stopped in my tracks by the music coming out of Kef Q speakers and a Linn CD amp.  I literally thought that band had started up in an adjacent room.

I was told at the time the Rega Ela 2s were even better, but that was not the case.

Thanks for the interesting posts.