The Shure V15 V with a Jico SAS/B stylus VS The Soundsmith Hyperion MR and Lyra Atlas SL

@richardbrand You were talking about balanced force woofers which are bipoles in the context of speakers which are dipoles. As you correctly mention 57s are dipoles. There is a huge difference. The dipole nature of panel speakers is not the same issue as dipole subwoofers if you remove the low bass from them. Like every other dipole woofer they stink at it. There rear wave of a panel loudspeaker, at least above 200 Hz is relatively easy to control, below 100 Hz  you are totally helpless. Unless you can get panel loudspeakers 10 feet from the front wall, in order to achieve the best image, the rear wave has to be partially absorbed by at least 50%. People frequently prefer the sound without absorption, it is brighter, more airy and louder. It is also far less accurate and at times painful (sibilance). @bdp24  As far as subwoofers are concerned, low bass is omnidirectional. The rear of the subwoofer driver is just as omnidirectional as the front. Take two enclosed subwoofers and play a 30 Hz test tone. Walk around the room. As you move the bass will get louder and softer due to room modes. As you get close to walls the tone will get louder. This is barrier effect. Now wire one of the subs backwards 180 degrees out of phase. Now as you move around the room the tone goes from almost entirely gone to extremely loud. Where this happens changes with frequency. An open baffle subwoofer is exactly the same as two out of phase subwoofers, actually worse because in open baffle designs the drivers are inadequately braced. Put your hand on one while playing a 20 Hz test tone at 85 dB. It will be shaking and that is distortion. At some frequency, depending on the effective mass of the system, it will shake so badly you will be able to see it. This is the resonance frequency. There is absolutely no way you can overcome this. You can only live with it and the best way to live with it is to avoid dipole subs like the plague. 

I think what Steve Guttenberg is trying to express is that playing full range ESLs will not go all that loud and because they are dipoles, the low bass is compromised. They are also very difficult to drive and the amps used make an extreme difference. Look at the monsters Roger Sanders uses to power his speakers. Once you take 100 Hz and down away from ESLs it is a whole different story. Roger crosses to his transmission line woofers at 250 Hz using a dBx driverack. Without those frequencies it is harder to saturate the transformers and the diaphragm has a lot more room to go loud, very loud given enough power. I have no problem hitting 105 dB, ear splitting levels. At 95 dB they might as well be playing at a whisper in terms of distortion which is an order of magnitude below any planar magnetic or dynamic loudspeaker. I guarantee "threadbare" would never be a term anyone would use to describe my system or Roger Sanders speakers including Mr. Guttenberg. If anything he would think my system had too much bass and my response would be to compare it to live performances and not other systems. The only problem with Roger's speaker is it is extremely selfish, it beams like crazy. People sitting outside the listening position get no direct high frequencies.  The ETs are good speakers, better than most, but IMHO the Magneplanar 3.7i is even better. That ribbon tweeter is fabulous, arguably the best tweeter made. The ET's tweeter is too wide which will cause it to beam.  I once had a pair of Tympany IIIs. It was with great fortune that I met my wife at this time giving any other speaker a reasonable WAF. She loves the Sound Labs as they blend right into the room. People don't even notice them at first. 

Every audiophile should read Roger Sanders White Papers. https://www.sanderssoundsystems.com/technical-white-papers

Every one of those subwoofers you mention is challenged by bad enclosures and their bass is colored.  There is no such thing as too many drivers in a subwoofer system. The more surface area you have working for you the lower will be distortion levels. INHO the minimum is two 15" drivers or four 12" drivers. 

@lewm A dipole cancellation compensation circuit? Talking about wishful thinking. How many bad ideas does it take to make a good one?

The subwoofer design you mention is just as bad as the open baffle subwoofer except the drivers are more adequately braced. Like the open baffle subwoofer the only virtue it will have is terrible bass. Using drivers in phase at opposite ends of a symmetrical enclosure cancels Newtonian forces, the enclosure does not shake and the drivers brake each other improving transient response. The drivers have to have high BL products and very stiff cones, preferably aluminum to prevent paradoxical flexing. You also want drivers with a shorter X max and stiffer suspensions for the same reason. 

OMG! I once owned Tympani 1Us and then Tympani IIIs. Those were my only forays outside of the ESL paradigm since 1973. Without the ribbon tweeter, magnepans were dead sounding, utterly lifeless. It’s frightening to think how closely our bouts with audiophilia coincide, and yet how profoundly we differ with respect to digital processing and room equalization.

@lewm  My assessment of the Tympanies matches yours. I also took a foray into ribbon speakers with the Apogee Divas, also a big mistake. It was back into Acoustat 2+2s until the Sound Labs came along. 

You mentioned being fond of live performances because of the dynamics. The only difference between us is I chased those "dynamics" using subwoofers. Once you realize (get hooked on) the benefits of subwoofers it is a very short hop to digital processing. You are already toying with the idea of subwoofers. I know for an absolute fact that if you listened to my system for just 15 minutes you would be 100% onboard. 

I’m on board and have been for years. I just don’t want the extra clutter and complexity. Whenever I get close to pulling the trigger, my inner self says, "Nah. My Sound Labs do excellent bass, though I would not argue that very low bass could be better. I just don’t care enough. My Bev system has better bass, as good as I could want. In my own opinion, a system I have heard locally with stacked Quad 57s that have been modified by removing the electronics and direct driven from EMIA tube amplifiers with only one transformer at the interface outperforms my long time friend’s Acoustat 2+2s by a long shot. But with those mods and upgrades to the Quads, this is no surprise. I think that Quad system may also incorporate subwoofs, but I am not sure. The owner demoed the system at the Capital Audio Fest (coming up soon) with the stacked pair. At home he uses stacked triplets. If he is there this year (along with Dave Slagle his close friend), I will report.

I did not quite say that I am fond of live performances "because of the dynamics".  I said that on the frequent occasions where we attend live performances, what is striking in comparison to any home audio system is the dynamics of live music, as opposed to pinpoint imaging, which was the subject of that discussion.  I once had a saxophonist come to the house and stand between the two SL speakers while playing a tune in our living room (aka, the listening room for the Sound Labs). Well, actually she happened to be visiting and had her sax on hand and was kind enough to play for us.  That was informative.

@mijostyn 

Have you managed to try out the recommended capacitive loading ( 250-300 pf ) on the Shure yet. I am interested to know the results.

Re Tympanis - I had a pair traded years ago, spent more time repairing them than listening. Fortunately found someone that thought they made very good screens for their parlour.