Thiel Owners

Not seen a Levinson 27.5 in recent times but can tell you I help deliver many moons ago Levinson amps with Thiels.  Should have no trouble driving them.  If one is in a large room and listens very loudly that is not to say that something that delivers more power can be more appropriate for them (but don't be fooled by the conservative power ratings.  Old Levinson 33Hs (helped deliver a pair of those - came with a free hernia - 220 lbs. each shipped with the crate), could drive just about anything (at least what I've seen and they didn't have excessive power ratings vs. many other things - very conservative).  With my old Thiel 7.2s (which are a harder load that the 3.7s), I did own Proceed amps (which were basically Levinson budget amps). and they drove them no problem.

@cascadesphil thanks for your feedback, yes the 27.5 doubles it's power from 8 to 4 ohms even if it's ont 100w it must have quite a bit of current.This guys who owns this Levinson 27.5 is interested in buying my 3.7s.

Figured that was the reason for you asking.  In my old house, before I had 3.7s, I had Thiel 7.2s.  The room was huge.  It was about 16x20 with a 19 foot ceiling that opened into other spaces. Easily the equivalent of over 7,000 cubic feet.  The 7.2s were rated at 86db (tested by one magazine I believe at 85.5) and the 3.7s at 90 (tested by one magazine at 90.7).  At one point I was driving the 7.2s with a Bryston 4BST and it was more than once where the amp went into momentary (literally a second) clipping (I have an integrated AV system so used it for both movies and music).  When I went to the Proceed HPA amp, it had plenty of juice to drive the 7,2s, which, are noted, were a much more difficult load than the 3.7s (subsequent to that I got a 15 amp version of a Bryston 14BSST to drive the 7.2s, which it could not and I ended up with 3.7s, which the 14BSST handled better as far as the impedance but not as well as a Modwright KWA150SE).  It's not your place with the potential buyer, but, with the changes in ownership over time with Madrigal Labs/Levinson some of the older amplifiers may not be supported by the factory for repairs.  I would think unless the person has a huge room and plays them insanely loud, it would not be a problem with the 3.7s.

There is a real limitation to dynamics in first order filters. On the one hand, there is no time smear or phase rotation in the crossover range for very realistic immediacy, but on the other hand, the drivers, especially the tweeter, do more work, generate more heat, and experience anomalies coupling to the air beyond their 'natural range'. Thiels are actually small-signal machines which do pretty well in normal rooms at normal volumes. But they are not and were not intended to be screamers.

In interesting with respect to two different design philosophies.  After a short exchange with the designer of the "Infinite Slope" of Joseph Audio in another thread, which optimized for frequency domain whereas time-phase optimized for time domain,  and "Prof" has listened to both Thiel and Joseph Audio, and he said he like them both.
I personally think there is a unique sound with first order that cannot be found in the higher order design.  Maybe "Prof" can further describe if there is any intrinsic difference between these two type of speakers.  

The ML 27.5 should be capable of driving the 3.7's successfully if not played too loudly in too large a room. More power could be beneficial.