Sorry, but that is not true. ESLs will move their diaphragms in an attempt to make bass and if you take a very near field measurement they would seem to be very accurate... until you move away from the speaker. Because they are dipoles there are interference effects that cause amplitude issues and wors, the longer excursions of the diaphragm Doppler distort everything else the speaker is doing. Not only this but the longer excursions severely limit headroom because the diaphragm has a very limited space to operate in, about +- 3 mm.
I cross at 100 hz because this takes all the long excursion frequencies away from the ESL increasing headroom and lowering distortion. My subwoofers are passive and use Corian layered with MDF for their enclosures. They are stiffer and heavier than any commercial 12" subwoofer. With digital bass management you can not identify the subwoofers and these are not as good as I had hoped. The next model is almost finished and will be a big improvement. I have been experimenting with subwoofers under ESLs since 1979.
Given your assessment I have to assume that either your Velodynes resonate unacceptably or there is something wrong with the Trinnov's programming. To crossover at 100 Hz you have to use a very steep slope, at least 48 dB/oct and it should be Linkwitz-Riley. I do not remember if the Trinnov can do this. All I can say was when I reviewed the Amethyst several years back I was disappointed in the flexibility of the bass management. Having said this, the only commercial subwoofers that are reasonably accurate are the Magico Q series subs. They are very expensive and HUGE. The best subwoofers otherwise are the Martin Logan Balanced Force series subs. They resonate less because the two drivers opposed each other canceling Newtonian forces. The Magicos do this also and there are two Balanced Force KEF subwoofers that are smaller than the MLs. I know you would be happier with the MLs under your ESLs. I will review the Amethyst's bass management and get back as to what I think would be the best way to set it up. If it can not due 48 dB/oct then you have to cross lower. You do not want the subwoofer getting into your midrange. At 24 dB/oct 80 Hz is pushing it. My old TacT 2.2X could do 80 dB/oct in 1 Hz increments from 20 to 320 Hz. And, you could change it on the fly. There is one simple test. Turn the main amp off and listen only to the subwoofer which are going to sound really bizarre. This is normal. You should not hear any voice coming through. If you do you either have to increase the slope, lower the crossover point or both.