Thiel Owners

If we had a sticky option, I would elevate Tom's description of thiel speakers to that status. It is fully consistent with my experience.
The 3.7 with sub woofers is an excellent system.
Tri-amping with eq for system and room effects has done wonders for my 3.5, coming very close to the 3.7 system. I can only imagine that 4-amping with eq the 5i would easily match the 3.7 with sub woofers.
By the way, I think that going with multi channel amp and DAC plus eq is essential to mitigate room effects, affordable compared to high end amp and solves most technical short comings of high end thiel speakers. It's fun too. 
I have settled on a 8 channel hypex ncore252mp amp, a laptop with Adobe audition software and a motu interface to conduct my experiments. 

So you guys are literally going around the internal crossovers? 
I don’t think I want to break into the speakers to set this up. But really could be amazing as long as you don’t overdrive one of the drivers by mistake.

@jafant @jafant  I’m not sure yet. Im looking at the ar9, kef 107 or 207, thiel cs 5 or 7, b&w 800 series, dunlavy audio, smaller apogee, sonus faber. Among others

thoft - among your short list, the Dunlavy is phase/time coherent like Vandersteens and Thiels. The others are not.

brett - I don't know how many of 'us' have ventured into DSP / active, etc.

"That bass affect" is present in all reflex bass alignments. The 3.6 passive is in proper polarity, pumping out when the woofer pumps out, but it is a whole cycle out of phase - 360° phase shift, just like other reflex systems. That same 360° phase shift is present in most "modern" crossovers which use 4th order filters on all drivers. The ear-brain compensates or learns the phase lag. But Thiel fans tend to appreciate the lack of that phase shift and resulting naturalness of zero phase shift through the crossovers.

Among Thiel speakers, those with sealed bass (like your Kappa 8s) include the model 01, 03, 03a, CS3, CS3.5, and CS5 plus the PowerPoint / PowerPlane with the 6.5" PowerDriver. The others have either ports or passive radiators.

@tomthiel, re: your earlier post re: bi- or tri- amping the CS 5's;  this would require modifications, 2 to 3 more outlets, 2 to 3  more shelves, 2 to 3 more power cords, 2 to 3 more pairs of interconnects, 2 to 3 more pairs of speaker cables. The extra  Benchmark's would still be limited to the Thiel minimum recommended 100 Watts per section. 
 With all due respect, I really don't put much stock on what a manufacturer claims off the record; let them put the specs in writing or provide third party measurements (interesting that Stereophile excused the Benchmark from full 2 Ohm testing, either in stereo  mode single channel, simultaneous dual channel stereo mode, or mono configuration measurements). While I do respect the Benchmark's low distortion specs, and especially the adjustable gain options, their amps don't read as suitable candidates for sub 3 Ohm loads, and are not exactly power houses above 3 Ohms. In that the Thiel's shallow 1st order cross-overs have so much more overlap than other networks, using identical amps for multi-amp use is of even greater importance. 
One used Krell FPB 600 costs about the same  (actually a bit less) as two used Benchmarks and can provide substantially more power to each and  every driver, without compromising frequency linearity into a speaker thirsting for power, and do so maintaining Class A operation the whole while.  One Krell seems like a much better match for the CS 5's.
 While with appropriate amplification ( the Krell KMA 400's are the best I've heard them with) I think the CS 5i's are on absolute terms the best sounding Thiel's ever made, and amongst the best speakers I've ever heard, including much more expensive alternatives. Without appropriate amplification they can be disappointing.  
I found your earlier posts suggesting reshaping the CS 5's baffles in order to simplify the cross-over as a more interesting/promising proposal.

P.S. I started this post some time ago. I've been a bit busy, but I hope to respond to your other inquires in the near future.