If I had been a smart person, I would have stopped with the ProAc D18’s and lived relatively happily ever after. Instead, like Forest Gump, I continued down the road, ultimately to see whether more money could provide greater musical purity than my $125 head phones and a more realistic portrayal than my departed Acoustats that I sold for $200.
The good news is that such speakers do exist. The bad news is that you may pay a high price indeed.
The high price listening experience cemented some thoughts I had with the less expensive models, namely that not only is there a point of diminishing returns, there are points of reverse value (kind of like the stock market L ).
I heard 12 models at $10k and above. The two described below retail at $10k. Of the 10 priced over $10k, only 2 were better overall than the 10k models: the B&W 802D (the best overall) and the Wilson Sophia 3 (an imaging wizard of speed and grace). Each of the very expensive models other than these shared one of two characteristics -
1. They had a single outstanding characteristic that drew attention to itself to the detriment / destruction of musical coherence.
2. They were dynamic to an unrealistic extent. Initially impressive, ultimately unrealistic.
To me, these speakers merely had an expensive form of distortion.

B&W 803 Diamond

The 803D is the Marilyn Monroe of speakers. It looks like a $10k speaker, even (or perhaps particularly) to those who know nothing of speakers. It’s curvaceous and beautifully finished, with a sophistication that shows its high-tech chops. Those with a technical bent can appreciate that what is inside is accomplished with an even greater degree of skill than the exterior.
The 803D’s height is adequate for listening position flexibility without being visually imposing, while its footprint is small enough to make it relatively unobtrusive. It maintains its overall sound quality very well at lower levels (unlike most large speakers), promoting a harmonious existence of music and conversation. While these may not be significant considerations for those with dedicated rooms, it’s far from a trivial trick to pull off, and one that the majority of high-end speakers more or less abandon in the quest for ultimate sound quality. The 802D, with its R2D2 look, obviously fails here for instance.

Speaking of the 802 - In their prior “Nautilus” version, the 802N was often considered the high water mark of the line. The performance gap between the 802N and 803N was considerable in almost every way, while the price difference was not. This tended to relegate the 803N to a second-class status, and perhaps that reputation has followed the 803D. Virtually all of the reviews / press / buzz has passed the 803D by, focusing instead on its big brother. That’s most unfortunate, as in most regards the 803D is close to identical to the 802D, and in a few actually betters its elder. Only in absolute mid-range articulation and low bass extension does the 803D noticeably bow to its larger sibling.

What it does right

The 803D can create believable musical events with each instrument or voice represented accurately both in location and frequency content. Most speakers around this price point excel at one or the other, but few do either with the skill of the 803D, which does both. Their portrayal and integration of bass instruments with appropriate size, tone, and dynamics is absolutely world class. Bass integration where the speaker’s response is reasonably deep is about the most difficult aspect to musical recreation to pull off, and the 3 Rohacell driver solution is about as good as anything out there regardless of cost. It also doesn’t seem to be particularly picky concerning room size, at least in my limited experience.
The Diamond tweeter is of the fast/accurate variety, and is one of the world’s best in my experience. While it doesn’t have the sweetness of the Paradigm Be unit, it has no obvious flaws. The mid-driver matches the tweeter’s speed yet does not discolor instruments and voice within its range to any notable degree. In this regard, no one does as well as the upper 80xD models.
If one’s requirements are domestic harmony and appearance with no compromise in sonic ability, the 803D’s are the best I’ve met.

What it does less than perfectly

With some types of music, there is a hardness to the mid-range that is not present in others. It’s most apparent with electric guitars and heavy rock and gives the impression that they’re not totally happy playing that sort of thing. IMO it may be a feature of the surround-less mid driver, though that’s a guess.

The 803’s do an excellent job of portraying objects (voices, instruments) in space, but perhaps are bettered in recreating the performance environment itself. They are not forward per se, but their image depth tends to start at the speaker plane, rather than creating a limitless stage. Of course, since most music isn’t created in an actual venue, or even exist acoustically…

Bass extension is not quite at subwoofer level, though it’s not far off. The cut-off is appropriate for allowing music and conversation to coexist, rather than distracting guests with the impression of imminent tectonic activity.

PMC Fact 8

If the B&W’s are Marilyn Monroe, the PMC’s are Clark Kent. If, in some alternate reality, Fact 8’s were sold at the local Wally Mart for $1000 the pair, they’d no doubt be totally outsold by the 5-way built-in subwoofer super-tower at a similar price point. While they’re nicely enough finished, there’s no getting around the Fact (excuse the pun) that you’re asked to pay TEN THOUSAND DOLLARS for a box-shaped two-way speaker with 5.5” paper “woofers” and a single non-descript tweeter. For virtually the entirety of humanity, that’s just not going to happen. Even for the true audio nut, at some price point, say $5k or so, one begins to expect some additional degree of complexity, sophistication, beauty, and maybe a mid-range driver. The Paradigm S6 provides that. The 803D absolutely exudes it.
It must be that the prospective customer is asked to pay this princely sum for the Fact’s amazing sound quality, since they otherwise would have no reason to exist, no? Fortunately, that hope is fulfilled, and in no small regard. While they may be performing some types of frequency and decay manipulation to accomplish what they do, as Bobby Jones said of Jack Nicklaus “He plays a game with which I am not familiar”.

What it does right

In short, the Fact 8’s can create a degree of musical reality that is unparalleled in my experience and that can, in Fact (sorry…) easily be mistaken for reality. A good number of speakers “open the window” on the musical event. With the Fact’s, there is no window. There is no sense of speaker or driver. There is no sense of multiple drivers, crossovers, enclosures, or any physical divorce from the recording. Instruments exist with tonal purity, accuracy, and delineation in a believable environment, free of the mortal coils of physical encumbrance. With appropriate recordings, the sense of being “there” is complete. Whether “there” is an accurate interpretation of an actual venue or event may be questioned, but not while the Fact’s are doing their dance in front of you.
High-end speaker by their accurate nature thrive with quality signal sources and material. They’re by definition needy of quality upstream components and recordings. With the Fact 8, that’s not the case. It has immense latitude for modest (or even rather poor) material and source quality. The actual reason for this may make one ponder, but the impression is that you can’t say that the speaker sounds good or bad with a particular piece of music, since in this case the speaker has effectively ceased to exist. A nice byproduct is that modest analog rigs sound quite nice indeed.
I don’t know exactly how they accomplish what they do, but it certainly isn’t by accident. There’s obviously a scary degree of skill and experience in play here. As others who have reviewed them have said, ‘it quickly becomes apparent that you are in the presence of something rather special‘. Indeed.

What others may do better

The Fact 8’s don’t have an uber-tweeter.
They are to a degree the opposite of the 803D. The B&W’s place clearly delineated representations of instruments in space. The Fact’s also create the space.
May be interpreted as somewhat “dark” sounding.
Don’t reach sub-woofer frequencies.
Can play loudly, but have limits.
Dynamic, but not normally in a way that overtly impresses as such.
May contain some form of auditory “happy drug” that’s enhancing reality.