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

What you are describing are precisely the benefits of big power. As you Americans say about car engines: there is nothing that beats cubic inches. Just imagine the amount of physical energy produced by a symphony orchestra. The speakers have to reproduce that, with an efficiency of perhaps 1 % (a proper calculation is beyond me at this time of the day). Even with such by audiophile standards relatively massive amplifier power, you can only hope to reproduce such a symphony orchestra at little more than postage stamp size (a domestic room will not allow anything more anyway). As you discovered, watts fortunately do not cost that much anymore.
As for thePX3 and PX5  successors of this amp, apparently their fans do not switch off completely, so they are less suitable for domestic use.

KEF LS50s are not bright at all. In fact, I was surprised to find they're warmer than all other speakers I've had in my system. I have Spendor 2/3s (often described as "pipe and slipper" speakers) hooked up to the same Yamaha amp as the LS50s. I can do an A/B comparison with the flick of a switch. The KEFs are no brighter than the Spendors. They're actually a tad warmer.
 

A pair of KEF LS50 sound exceptional for their price.   Quality stands are required for their proper performance and this additional purchase must be calculated into the purchase cost (got my KEF branded stands off Amazon as well as the extra dampening stand fill).  The LS50w self powered is another path to consider and would remove any amplifier issue (return the Yamaha).  You would have a system that would not disappoint in its musicality.  I have a set of the standard LS50 that when placed into my main system always amaze me with their performance.  

I'm passing along some info I have been gathering on these various speakers.

The TANNOY Revolution XT 8F is one of the speakers that was recommended to me here. Below are some quotes I pulled out of reviews. I was looking specifically for critical quotes regarding the higher frequencies.

The first comment below concerns me a little bit, even though most of the reviews are very positive.

https://www.whathifi.com/tannoy/revolution-xt8f/review - "Tonally, these Tannoys aren’t the sweetest sounding performers around. You’ll have to take care not to partner them with anything that sounds overly forward or harsh, because they’ll do little to tone these qualities down."

"We’re pleased with the stereo imaging. These speakers shine when placed well out into our test room and given just a touch of toe-in towards the listening position. Once the Tannoys are positioned with care their sound stage is crisp, nicely layered and pleasingly solid."
"give them a larger room to play in and the XT8Fs will shine."

https://hometheaterhifi.com/reviews/speaker/floor-standing/tannoy-revolution-xt-8f-floor-standing-sp...
"My only sonic critique of note is that the Torus tweeter’s lower treble seemed slightly less delicate and precise than my reference speakers’ ceramic-graphite tweeters. I noticed the difference primarily in the effects in “Welcome to the Machine,” panned between the side surrounds (which use the same ceramic-graphite tweeters) and the front channels. Also, cymbals sparkled but their shimmer didn’t decay quite as cleanly. While the difference was noticeable, it did not detract from the immense enjoyment the XT 8F trio brought me on every piece I played through them."
"Often, playing full-throated female vocals loudly will expose a speaker’s crossover points, as the tweeter or (more rarely) the midrange audibly compresses at the bottom of its range. With the XT 8F, there was no sign of overload no matter how hard I pushed."
"tape hiss was lightly accentuated by the Tannoy Revolution XT 8F compared to my reference speakers"
"Few if any similarly-priced speakers offer the Revolution XT 8F’s heady combination of top-notch full-scale sonic performance, attractive design, and excellent build quality. Highly recommended."

http://www.theabsolutesound.com/articles/tannoy-revolution-xt-8f-loudspeaker/?page=2
"Time and time again, the 8F was able to decisively reveal amplifier differences, a testament to its resolving powers. For the record, it gave its best imaging performance when partnered with tube amps that also happened to flesh out the most convincing spatial impression."
"The Tannoy Revolution XT 8F was Robert Harley’s top discovery at the 2015 Consumer Electronics Show. His first impression was as follows: “After listening to it and looking at the real wood enclosure, I guessed the price at $7000 to $10,000. The Revolution XT’s price was then revealed to be just $2600 per pair.”
"The Tannoy packs a virtuoso midrange that is competitive with speakers approaching $10k retail."

http://www.hifiplus.com/articles/tannoy-revolution-xt-8f-floorstanding-loudspeakers/
"I guess, when it comes down to it, I want my system to entertain, not to impress. I’d like it to do both, of course, but that tends to cost considerably bigger bucks than are being asked for here. Any loudspeaker selling at the price point of the Tannoy, or even considerably more, is going to have some defining compromises, and the temptation for many makers will be to take care not to offend."
"In some respects, the Tannoy comes across as the antithesis to something like the, broadly similarly-priced, Monitor Audio Silver 8s that I reviewed a few issues back. The MAs are very good loudspeakers that rarely put a foot far out of line. In comparison, the Tannoys are somewhat more bullish and, perhaps, a little uncouth, but they sure know how to have a good time. If the MAs are a well-trained Labrador, honest, reliable, and solid, then the Tannoys might be a Springer Spaniel, loads of energy, fun, and boundless enthusiasm, but prone to knocking over the occasional vase. Neither speaker has the monopoly on rightness, nor any fatal flaws, but you’d be unlikely to find that both will float your boat equally, and much will depend on personal taste and preference."

Here are a few quotes from reviews of the KEF R900. Again, I was looking specifically for quotes related to my goal of "smooth, sweet, soft, silky treble" and "shimmery, airy cymbals". Since violins can be a challenge, I also looked for any mention of those.

In particular, if the review mentioned anything negative in this area, I grabbed that quote.

Everything Audio Network: Audiophile Review!KEF R900 3-Way TowerMatched-Pair Loudspeakers“Impressive High-End Sound” http://everythingaudionetwork.blogspot.com/2016/03/audiophile-review-kef-r900-3-way-tower.html
  measures 44.5-inches tall, 9.4-inches wide and just over 14-inches deep. They weigh a manageable 65 pounds each.
  The top-end was never hard or edgy; the aluminum-based mid-frequency driver delivered a quick, tonally correct midrange — without exaggeration or hollowness.
  The drum cymbals and piano tone are spot-on delicious. The metal dome tweeter effectively radiates the top end of those wonderful cymbals, yet no stereotypical edgy or resonances.
  The speakers don't have that ultra low-end like some of the double driver, tower speakers I have listened to, but they are very good for music.
  the R900s produced the violin and accompanying orchestra with convincing authority. The balance of the R900s created a clean, immersive tone with lots of violin harmonics getting through. Reminds me of the excellent, metal-dome RBH-loudspeakers I have auditioned in the past. And as with the drum cymbals, the violin’s upper-end energy was not hard sounding. It was, er, just right, to borrow a phrase.
  The KEF R900 speaker is a well-conceived, three-way tower that performs well above its price point. As a stereo pair, the speakers offers a balanced symmetry with airy highs, a very good midrange and ample low-end with nary any bloominess. If you are into a true, sonic picture of the source audio, especially hi-res music, the R900 is a speaker to consider. You need at least a medium-size room to enjoy its virtues.

6moons audio reviews: KEF R900 http://www.6moons.com/audioreviews/kef3/1.html
KEF R900 Loudspeaker Review | StereoNET https://www.stereo.net.au/reviews/review-kef-r900-floorstanding-loudspeakers
  Mids, and especially vocals, are pushed ever so slightly forward in the presentation. Highs are very well extended, but don’t push too far forward into the mix to be overbearing
  Unlike many loudspeakers, I actually found the R900 to not be overly fussy with speaker positioning.
  Those who do not have ideal listening conditions or rooms - fear not. The KEF R900 is not a fussy, directional monster.

KEF’s R900 speaker | Stereophile.com https://www.stereophile.com/content/kef%E2%80%99s-9000-speaker
  a bit of tinny-ness on top and booming on the bass.

KEF R900 Loudspeaker | Hi-Fi+ http://www.hifiplus.com/articles/kef-r900-loudspeaker/
  they are so dynamically and tonally consistent that they are almost impervious to level, going loud or quiet with equal ease and a totally absence of dynamic collapse or strain.
  the bass is light on its feet, transparent and tactile, placing notes and giving them shape in a way that you’d normally expect from a far more expensive system and speaker. That clarity and sense of musical purpose extends up the range, embracing a fluid and expressive mid-band before reaching the clean and extended upper frequencies. The Uni-Q’s tweeter might not possess the sheer speed and resolution of Focal’s beryllium units or the almost reticent smoothness of the more affordable diamond drivers, but it more than makes up for that with sheer continuity, providing a natural extension to the midrange that is indistinguishable in cast or character

SoundStage! Access | SoundStageAccess.com (GoodSound.com) | SoundStage! Access | SoundStageAccess.com (GoodSound.com) - KEF R900 Loudspeakers https://www.goodsound.com/index.php/equipment-reviews/456-kef-r900-loudspeakers
  The R900’s tweeter warrants an ovation and a comment. It took over cleanly and effortlessly from the Uni-Q midrange, giving nary a hint that I was hearing two different drivers. Such unity of sound is found elsewhere, but almost always at higher prices. Furthermore, the tweeter sounded smooth throughout its operating range, without the edge that some metal domes can have. Nor was it smooth in the way of, say, speakers from Sonus Faber, whose characteristic smoothness can obscure a recording’s finest details. Rather, it was smooth in its reproduction of the finest details. In doing so, it helped paint a quite transparent soundstage -- as in James Levine’s performance, as pianist and conductor, of Gershwin’s Rhapsody in Blue, with the Chicago Symphony (16/44.1 AIFF, DG Deutsche Grammophon): I heard clean through to the back of the stage, with no haze or ambiguity to muddle through to hear the players. Partial credit is due here to the Hegel H300, whose preamp section is as quiet as its amplifier and DAC are resolving.
  My comment on KEF’s aluminum tweeter has to do with its ability to play well past 20kHz. Whereas other tweeters' tendency to peter out at or before 20kHz exhibits itself as a relaxed or unobtrusive top end, the KEF sounds as if it remains flat straight on through this threshold of human hearing. From my very first listen to the R900s, I heard a top end with copious extension, but extension that wasn’t exactly laid-back. It wasn’t bright or edgy, but leaned slightly toward that end of the audioband.

Compared to Vivid Audio’s V1.5 two-way speaker ($7500/pair), however, the KEF R900’s overachievement reached a ceiling. The diminutive V1.5 uses the same tweeter (though not the same tube loading) as Vivid’s flagship Giya G1 ($60,000/pair) -- a catenary aluminum dome whose output extends all the way up to 39kHz, ±2dB. While the V1.5’s single 6.2” midrange-woofer couldn’t hope to match the bass reach of the R900’s twin 8” cones, the Vivid was superlative through the mids and highs. The V1.5 produced greater transparency, a more effortless, organic sound, and even greater resolution than the R900.


Premium Performers: KEF R Series Loudspeakers Review | High-Def Digest https://hdgear.highdefdigest.com/34168/kefrseriesloudspeakers.html
  If you're looking for premium speakers to fill your home theatre and handle a variety of musical genres, you can't do much better than the KEF R Series. Transparent. Well-rounded. Superb rendering and imaging at all volume levels. A powerful-yet-compact subwoofer. Fantastic in pieces, but as a complete sysem your home will sound better than your local movie theatre. There's almost nothing to nitpick, though badly compressed audio might reveal itself, and prepare thyself to declare war on dust.

Amazon.com: KEF R900 Floorstanding Loudspeaker - High Gloss Piano Black (Pair): Home Audio & Theater https://www.amazon.com/KEF-R900-Floorstanding-Loudspeaker-Gloss/dp/B007Q6Z5MO
  Finally have a set of these after running through pretty much the entire R range. These are the best by a long way. It's not close. Don't listen to anyone telling you the R500s image better. They don't.

KEF R900 Speakers https://www.audiot.co.uk/products/kef-r900-speakers-4651.aspx
  They require considerable current capability from the amplifier to deliver their best and therefore need to be partnered with excellent electronics.