How much do you have to spend?

Don’t think you can answer the question this way; starting out with money.  Music satisfaction is the goal, not budget.  How much you end up spending usually depends on what is pulling at your heart strings at that moment, be it amp or source or cables.  
A pragmatic approach is to start out with the biggest variable, speakers.  We all love something different, new or used.  Having found the speakers, we now look for an amplifier with the matching characteristics needed to drive our chosen speakers. Cables to hook them up and on to preamps and sources.  Eventually we have a system, understanding we’ve some errors and corrected along the way.  Then and only then can you add it up.

In my experience the sound quality of each component overwrites the next item, so it is best to spend a large amount on the Power amp first and then speakers. The pre-amp and source according to taste.

With me cables and power distribution are important so a good 20% has to be spent there. Along with supporting furniture, I build my own.

With all these things you have to audition up and down scale as price is not a precursor to success. I owned a Peachtree iDac this had a galvanic isolator and so I used an AC PSU. This gave me one of the best reports I have heard. So just go listen and learn.

The Power Amp and Speakers are most Important .. approx 25% on the amp and 15% on the speakers would be good, the amp will open up these and provide a good conclusion

IMHO, diminishing returns applies more to electronics (assuming those electronics are not flawed) than to speakers and phono cartridges. Speakers affect the sound  more than any other single component.
I own Ref 3’s, upgraded from R11’s. While a similar overall sound, significantly cleaner & clearer & well worth the investment. Speakers should IMHO be your largest investment by far, with substantially less diminishing returns. 

I don't know much about NAD, or never heard anything exciting about them that would make me try them. KLH speakers, yes, but I agree with the comments above, it's a too many tricks pony, it would be first to replace on my list.

Naim Uniti Atom all in one everything,$3500 do $3500 for speakers you are done if you stream only..