How much do you have to spend?

Those were all msrp prices so, yes, used would be 50 to 60K.  

$30k to $100k is a big spread.  My system falls between the two. 

That's what I said in the beginning - $100k new, and then $30k minimum standard.

You can get a reasonably good sound for less, especially for smaller rooms and if you don't listen to large scale music, but we are talking audiophile standards not simply good sound. Actually, that's what I have - good sound but below my own minimum audiophile standards. It was probably $15k new but I am not sure, I bought almost everything used. 

@fritzenheimer Your KEF setup is really good, and I had the same thing but 1 sub. I am not a fan of the NAD gear. I would keep the KEF gear and add a better amp and DAC.

I tried the following with the KEF gear, and it was very good.

- someone on eBay is selling my old KRELL amp that I used with the KEF speakers. I love this amp and was sad to see it go.

Krell Duo 175 XD Stereo Power Amplifier Black EXCELLENT | eBay

- CODA #8 and #16

- Schiit Wotan amp, I did not try this on the KEF, but I did on the Maggies that are hard to drive. It would be very good on the KEF

If you are on a budget the new Schiit Singular DAC (Byggy) is really good. I sold it to buy the spectacular imersiv D-1 DAC. The D-1 maybe overkill for the KEF but the Byggy DAC would be terrific.

All of these would be my choice over the NAD.

BTW - I am selling my CODA #16 amp and switched to the $995 Class D Audio GanFet 6.5 amp for my office Maggies. Now the #16 is better but the greatness of the #16 cannot really be appreciated by my Magnepan Mini speakers in the office. The Class D Audio GanFet 6.5 sounds better to me than the NAD. Nice and clean with a bit of body. 

Home Class D Audio - Class D Audio

If you spend the majority of money on your speakers & choose a pair that are fairly sensitive & easy to drive (minus extreme impedance & phase swings) you can get away with spending much less on surrounding equipment while getting great results. 

Upgrading to the KEF 1's is a legitimate upgrade. Even objectively they are superior & should give you instantaneous perceivably differences from your LS50's. 

Personally I would also focus on acquiring an integrated that works in the analog domain only. Separate your digital & analog components. Low noise components. An external Dac & external DSP for the subs. The LS50's do have their limits though..I can understand wanting to trying something legitimately better.