Thiel Owners

@bobscliff, the CS 2.4's impedance drops to below 3 Ohms. You're not likely to find many amps spec'd to the 2.4's specific minimum impedance. One might find some amps spec'd to 2 Ohms. If you want to get what that the 2.4's are capable of you'll want an amp spec'd to a minimum of 400 Watts into 2 Ohms. If the amp is not specifically spec'd into 2 Ohms, it 's not very likely that it's capable at that load. Being "stable" into a load only means that the amp won't go into oscillation into that load. It is not a guarantee of performance.

"If the amp is not specifically spec'd into 2 Ohms, it 's not very likely that it's capable at that load."  That's not true 100% of the time (and I realize you indicated 'not very likely').  For example, the IcePower AS series (1200AS) indicates minimum inpedance of 2.7 ohms.  That derives from the pro market where someone may be piggy backing three 8 ohm speakers.  I had both an IcePower 1200AS stereo and dual mono amps and they drove (and sounded better too) my Thiel 3.7s than my Modwright KWA150SE in my system.  There are two magazine reviews.  One measured the minimum impedance at 2.4 ohms (at 125Hz) and the other at 2.3 ohms (at 120Hz) and both measurements indicated the impedance remains between 2 and 3 ohms throughout most of the audio band (the Stereophile plout shows something around 75Hz all the way up to around 20,000 below 4 ohms).  I now have a modded LSA Voyager amp and it was no issues either.  I also for a bit (since my system is an integrated A/V system) had a Class D Audio mini GaN amp driving the 3.7s for HT.

Peachtree Audio has a 4 ohm rating and indicates "The amplifier in the nova300 is capable of driving an extremely wide range of speakers with impedances as low as 2.5Ω and as high as 16Ω"  So that should be fine with the 2.4s (as long as there is not something else crazy in the chain such as speaker wire causing an issue with that minium impedance - many moons ago I had an issue with a particular brand of speaker wire driving Mirage SM-3s which were not a hard load).  The Yamaha noted by the OP, like many receivers, has an impedance switch for lower impedance speakers.  I converted my front bedroom system to strictly a UHD HT (vs. an integrated A/V system) and the Onkyo receiver has a setting for lower impedance speakers (the only thing rated less than 8 ohms I use in the 9 channels is the Ohm Microwalsh Talls I have for front Atmos speakers and the room isn't big so I just left the settings as normal).

My 3.7s are in a large room that opens into other spaces and I can play it loud enough with no distortion and no issues.  Sometimes, when my friend comes over during the week he asks me to lower the volume a drop.

@cascadesphil, but how much power are these amps delivering into 2 Ohms and at what levels of distortion?
 

To my knowledge, I don't know of an independent lab testing the full specs.  There's a review (without measurements) by a member of the SF Audiophile Society and he notes about its 2 ohm rating "“2 ohms stable” (not sure exactly what that means?)"

I'm also not aware of an independent lab test of my old Modwright KWA 150SE.  There's a review I saw that indicates a 4 ohm minimum impedance but there are no accompanying measurements.  My old (before the Modwright), Bryston 14BSST has some (but not much) actual measurements 2 ohm (Stereophile) but not with lots of watts and the Bryston was rated 600W into 8 ohms and 900 into 4.  I had Thiel 7.2s before the 3.7s.  The 7.2s were a harder load.  I had to build a custom amp stand with fans for the Bryston and the Modwright still got very hot but did not shut down into protection mode like the Bryston.  The Modwright got a drop less hot with the 3.7s,

So all I can tell you from real world experiences (and the room in my old house had 19 ft. ceilings and opened into other spaces) about problems or lack of driving my Thiel speakers.  When I sent inquires before and after getting the 14BSST lightly used they danced around my questions.  They also made a 20 amp version of the 14BSST (for low impedance speakers but I just had a separate (on its own breaker and receptacle) 15 amp circuit for the Bryston.  So that's should be a clue that in my situation with a huge room (probably over 7,000 cu ft) the 14BSST 15 amp version was not capable of handling the impedance.

So in the real world in my system (Modwright LS 36.5 DM preamp) all I can tell you is what sounds better (and not my opinion as I've had several other people over who agree) and drives my speakers better.  The Modwright amp would get hot enough that it would hurt touching it even though the heatsinks were inside the case.  If one goes to hifishark, there's a used Modwright listed for an asking price of $3,150 including PayPal fees and the amp is a current model that now lists for $11k.  I've noted before that audophiles, manufacturers and retailers tend to stick to conclusions about new technology (and it's not unique to audio) well past the actual performance of this newer technology.  The guy I sold my modded dual mono IcePower amp was buying it to power woofers and had also previously owned the Modwright amp and would probably have substantially similar conclusions about its sound vs. what I have (and it's in a different system in a different room).

So all I would advice anyone is to take advantage of any trial period (and break in the amp), assuming it has one and give it a try.  You might be surprised. I was shocked with my first Class D stereo IcePower amp.  A friend asked about Class D and last I heard (a few years prior) them they had gotten better but I wasn't sure if they had come of age.  I told him I'd get one and use it in a secondary system.  I broke it in using a secondary system of Ohm Microwalsh Tall speakers (augmentated by a Rel Strata III sub, a Meitner MA-1 DAC and an Odyssey Candela preamp.  I had a Bryston 3BST amp in the system.  I was in shock out of the box what a huge difference there was vs. the 3BST and even more amazed when I put it in the main system.

Keep in mind @unsound listens very loudly, peaks at 105 dB. Most Thiels are certainly going to need a boatload of power 2-4 ohms to reach that level. If I had that listening preference, I would pick different speakers.

If you listen to Thiels at more typical levels, it opens up many options. IMO, test results of steady state signals are , at best, a guide. It’s fair, I think, to look at the measurements and conclude a 10 W SET is a poor match for the CS5. But there is a wide middle-ground where you might let your ear be your guide. Here are the measurements for my amp which @unsound has informed me is a poor match for the CS2.4 despite, apparently, never having listened to the combo:

https://www.hifinews.com/content/ayre-ax-5-twenty-integrated-amplifier-lab-report