Looking for speaker recommendations that I can purchase on Amazon.com

"Personal Preferences: I am looking for non-fatiguing, warm, musical qualities. In another discussion topic here on this forum, @mtrot and I agreed about "smooth, sweet, soft, silky treble" and "shimmery, airy cymbals" as goals."

Sorry, but I don't think there are too many people here who'd read this and then recommend a "professional" grade amp.  Pro amps are generally made for durability, affordability, and overall power delivery capabilities -- not refinement.  Almost the polar opposite of what you're looking for.  The reason the 5000 was priced similarly to the 3500 is probably that the 3500 uses a transformer-based power supply and the 5000/7000 use a switching power supply -- probably for cost, efficiency, and weight savings, not sound quality.  I think you may be fighting an uphill battle reaching your goals with this amp.  I'd dump it and move on to a more synergistic amp/speaker pairing for your specific tastes and goals.  Sorry to be the bearer of negative news, and best of luck. 

"I’m happy with the Yamaha P5000S."

Yes, of course you are, because you’ve compared it to a Sony receiver. My 1985 NAD receiver would be a big improvement over what you have. The key question is this -- how does it sound relative to a truly refined home audio amplifier? I challenge you this -- buy this Yamaha integrated on Amazon and compare it to what you have...

https://www.amazon.com/Yamaha-S2000SL-Natural-Stereo-Amplifier/dp/B001M9G6I8/ref=sr_1_1?s=electronic...

You were sold sold a bill of goods by Willemj who thinks "pro" audio gear measures the same as home audio gear so it’s the same but just a better value. PHOOEY!!! He admitted the 5000 uses a switch mode power supply, but unless implemented with higher end engineering and parts, a crap switch-mode power supply (as would certainly be used in a relatively cheap "pro" amp) will make a HUGE difference in the quality of the sound you hear. They use cheaper components in pro gear because they have very different goals than with home audio. Look at the 3500 you’re asking Willemj about because it has a better power supply. Yes it has a better power supply, but look at the capacitors, power supply, and other components the Yamaha AS2000 uses versus what’s used in the 5000 or even the 3500. There’s a reason there’s very little crossover between "pro" audio electronics and higher-end home audio equipment. Very few people here would recommend a dedicated "pro" amplifier over one manufactured for home audio use. They’re just two totally different use cases, so trying to buy an "audiophile" quality "pro" amp on the cheap is largely just a fallacy. Otherwise we’d all have "pro" amps, right??? Or are we all here just absolute idiots who like to pay more for absolutely nothing except nicer cosmetics?  Ehem. 

Take my challenge -- PLEASE. The Yamaha integrated I’m recommending is manufactured to a completely different standard on every level versus the 5000 you have (or even the 3500). Call Yamaha and I’m sure they’ll give you an exhaustive list of differences between the two and why they’re improvements for home use. Hey, if you can’t hear the difference, just return it!   No harm done.  But I seriously doubt that will be the case. Even the Polks will be good enough to show you the improvements. The KEFs will do even more so. Hey, what do you have to lose?  Best of luck.

Oh please, regale us with your all-knowing test.  This industry is rife with studies that tell us our hering is wrong, and I'm sure this one is irrefutable too.  I'm squirming with anticipation.  

Listen, you're clearly an Amazon consumer so you know how it works.  Buy yourself the Yamaha AS2000 I listed earlier.  If it doesn't smoke the 5000 you have, just return it.  But, give both at least 100 hours of burn-in time or you'll not hear the best of what they can produce.  No less than Peter from PBN Audio has endorsed the AS2000, so buy with confidence if you also hear the difference.  Or just go with Willemj, who is clearly a measurement expert.  

I'm out.  Glad you're happy with your amp and best of luck finding speakers that work for you.  Enjoy the music!