~$6K mini-monitor recommendations?

What do you expect to get that the Kef LS50 can't deliver? I think you will just be throwing money away.

I think the same thing. I am going to both upgrade my electronics to use with my LS50's and also buy a bigger "bookshelf" speaker to keep in the same office as the LS50's,  the Yamaha NS5000. The Yamaha is much better than the LS50's ($15k)  and also has a almost full range sound. Crazy as this sounds I plan on placing the LS50's on Isoacoustic stands and place them on top of the NS5000 when in use, otherwise on a side bookshelf.

I am keeping the LS50's because it is an incredible monitor and I will use it until it falls apart. I do know that better electronics brings out the best in the KEF's.

BTW - If you are set on up grading and like the LS50 sound the KEF Reference 1 is a great choice. 

Never heard them, but always heard good things about the Genelec 8300 series if true near field monitors are your goal.

I second the harbeth p3esr I have the 40th anniversary and I use a sub but for near field they have a surprisingly good bass response on them so a sub shouldn't be needed. Plenty of reviews most recently from zero fidelity.  

If you can find a pre-owned pair of Wilson Audio TuneTot they sound really good. 

Take a look at some of he Sonus Faber stand-mounted speakers. These are not usually abused so buying used makes sense. You can find Electa Amators (series I, 2, and even 3) used, for around your stated price range. High WAF is a bonus!