I just bought these, and thought I would do a quick editorial review and commentary. My apologies since it will be entirely subjective, since I am not sure there is really any "objective" way to measure or describe these speakers--at least not, the important thing about them. Skip to the end for the tl;dr.
After reading all of the technical whitepapers and such, I finally broke down and bought one of the last remaining new pairs still in the wild. I waffled a bit due to a few concerns about various measured technical issues, particularly tweeter compression, but I finally pulled the trigger, since it was becoming increasingly clear it was now or, quite possibly, never. I would not be surprised if Polk never does a production run. That would be unfortunate.
After ordering up a pair in the walnut finish, about a week later a giant pallet with two boxes, each large enough to hold a small refrigerator, arrived at my curbside. After digging out a hand truck from the shed and gingerly walking the 150 pound boxes--consisting of 120 pounds of speakers and 30 pounds of packaging--up my front porch steps, I carted them inside and began the unpacking process. It takes a bit, because the speakers are huge, but the ingenious and intelligent packaging design makes a job that could have been horrific entirely manageable by one person. After extracting them from the boxes and shuffling them properly into place about 6 feet apart, I fished through the audio archives of my attic to find something to feed them a source. My primary two channel system has been dormant for entirely too long, and lay in bits and tatters. Kids, projects, too many commitments, and all that.
First, I needed a preamp. I had five or six to pick from, but grabbed my trusty old Technics SU-9070, and pressed it back into duty. This was one of those "golden age" components which is entirely under-appreciated. I've owned this sample for over 20 years now. While it is built like a tank, expensively built, and nicely engineered even by today's standards, would it still work? The switches were a bit scratchy and could use some deoxit, and the whole thing could probably use a good recapping, but it seemed okay. Unfortunately, the volume knob is a bit scratchy and being a sealed multi-gang Alps Black unit, may not be serviceable. Hopefully that cleans up. If not, I may pop something else into its place temporarily. Criminally, this is ultimately getting replaced with an AVR with room correction, which is en route. For purity's sake perhaps I'll set it up with a "real" front end as well. We'll see how it all works itself out.
For a suitably large amplifier for speakers the size of small coffins, the similarly massive Parasound HCA-3500 would do just fine. The Polks need lots of power from a common ground amplifier, and this 100 pound pig has that in spades. I hauled it out of some pawn shop ages ago when it was about a year or two old. I'm sure there's an unfortunate story there. The HCA-3500 is basically a two channel version of the current JC-1. Or, perhaps more accurately, the old version of the current JC-5. Parasound has never actually reengineered much of anything over two decades. They just swap out components and faceplates. There might be a bigger transformer here, or a few extra paralleled output devices there, some tweako resistors over yon, and revised circuit boards everywhere, but the dirty little secret is that all of the important bits have never changed
much. Except one--there is excessive second harmonic distortion due to a transistor manufacturer deviation from specs in, I believe, the gain or driver stage. I have the write-up somewhere, but I've never gotten around to switching out the part. Audible, I don't know. But I bet all that second harmonic makes it sound "tubey"!

It does show up in measurements. But let's get back to the speakers and end the suspense. At least
some discussion of the amplifier is necessary, though, since internally bridged amplifiers will not work properly. All driving current must come from the red speaker terminal and none from the black for proper SDA operation.
Speaker wires were connected up to the old Parasound brute, the SDA cable run, and finally the power switches (plural) on the beast amplifier were ready to be flipped back on for the first time in a few years. Engage. Protect light. Ack! Check the connections. Try again. Success. Now, were I doing this right I would have paid more attention to setup, room treatment, and all that good stuff. But this was hurry up and play with new speakers time! Now for some tunes. Uh-oh. Cell phone through a 3.5mm jack? Nah. An old DVD player and some CDs would have to do, for now. Good enough. Peter Gabriel, original 1986 CD (or therabouts). Play.
Wow. What is
this? How?! The superlatives that were hurled at these after their introduction were justified. This is an
experience. And it ain't like the "experience" you get from whatever nicely measuring pair of speakers that have been Klippeled to death. That's a great experience too, but this is next level. This is some serious what-is-happening-right-now-OMG-what-is-going-on level stuff. Grin and giggle stuff. I've only had an hour with them, but that hour was possibly the best hour I have had with a pair of speakers. I think the reason no reviewer has these in their "reference" system is because they can't. These speakers are not even playing the same game. They make "regular" speakers sound boring and broken. I disconnected the SDA cable and while the speakers were still fabulous, all the
magic was gone.
It is very difficult to explain just what these speakers do. An analogy to light is perhaps helpful. If a speaker were a flashlight, most speakers light up the area between them. The Polks do not do that. Like a flashlight pointing out, the Polks evenly illuminate everything in front of them--including to the sides. It's like adding a center channel and front wides that aren't really there. A 15 or 20 foot wide soudstage from speakers placed 6 feet apart, with no gaps in the soundstage. All this from a speaker 6 feet apart and me 8 feet away.
How is this possible? I shut my eyes, pointing to where I heard various sounds and instruments emanating from (all of which sounded quite natural), and then opened my eyes. I was pointing
well past the outside edge of the speakers. Yeah, you need to keep your head in an absolute vice to make it work. But it's worth it. Pinpoint imaging, uncongested neatly arrayed soundstage, all the typical audiophile nonsense--but now it makes
sense. When speakers are only throwing an image as big as they are apart, how does any of that nonsense make sense? It doesn't. But here, it does. This is like a full blown front stage with a left, right, center, left wide, and right wide. From two speakers pulling it off acoustically and not via whatever Dolby has in their latest algorithm.
I
almost caved and bought Revel Salon 2s. Glad I didn't. I already have plenty of nice, flat measuring, well-behaved speakers in various other secondary systems or the theater setup. That's an incremental improvement. More Tonal Balance! Ooh. More "Inner Detail" (whatever that is)! Ahh! A little more shimmer on that triangle, or a bit for boom from the bass drum! Eh, sure. The Polks have plenty of that, but again, this is a different ballgame, and when I only have an hour a week (although now I might have to make more) to "seriously" listen to 2 channel (and usually don't, because it is a bit boring), I would rather spend it with these weird looking things with their one-of-a-kind party trick. Calling it a party trick sells it short. They're doing what every other speaker
wishes it could. What I've been wishing speakers could do for many, many years. What I, at one point, believed they could do based on the florid nonsense in the audio rags. None of them ever could, but these actually can.
A fair warning though, these speakers are only for
you. 180 degrees off axis, it's ... weird. Out of the perfect center, and it falls apart. But on axis, it's just sublime. And if for some crazy reason SDA is not for you or you need to entertain a crowd, just yank the SDA cable and you have a speaker at least as competent as anything else Polk has ever made, if not more. But once you hear it, you won't unplug that cables. Cables in audio are often described as having magical properties. There is nothing magic inside of Polks cable, but it helps to create magic in a way nothing else I have ever heard does.
tl;dr: Great speakers. Unique, and amazing. Buy before they are gone, possibly forever.