https://www.stereophile.com/content/thiel-cs37-loudspeaker-specifications
https://www.stereophile.com/content/thiel-cs37-loudspeaker-measurements
Note that the sensitivity is spec'd as:
90 dB / 2.83 V/m (not 1 Watt)
the sensitivity is measured as:
90.7 dB 2.83 V/m (not 1 watt)
Note that the minimum impedance is spec'd as:
2.8 Ohms
the minimum impedance is measured as:
2.4 Ohms
This means that the equivalent "efficiency" as when using 1 Watt will probably closer to <86 dB.
Note that the only times the impedance rises above 4 Ohms (and then only in the deep bass region) it's met with rather challenging phase angles.
Note that through much of the bass and lower midrange that the impedance is below 3 Ohms.
Note that between 60 Hz through 20 KHz the impedance is always below 4 Ohms.
Note that Thiel recommended between 100 and 600 Watts per channel. That recommendation is based upon the standard 8 Ohm amplifier rating, with the understanding that the amp would double down as needed. If one wanted to do this comfortably without amplifier strain, being able to double down to 2 Ohms would mean between 400 and 2400 Watts into 2 Ohms. Why do you think Jim Thiel used 600 Watt Krell's with the 3.7's? See Pages 16 &17 in the link below:
http://www.krellonline.com/assets/support/FPB_ORIGINAL_SERIES_MANUAL_V982.pdf
The more recent Thiel's are a bear to drive, limiting appropriate amplification to those well engineered products that are up to the task.
The job of the amplifier is to power the speakers. Limit the search to those amplifiers that are capable of the work required, and then choose your preferred sonic signature. Anything less is compromising the work that went into developing these speakers, and the potential to fully deliver what they're capable of.
Something else to consider; underpowering speakers, and especially those with 1st order cross-overs might lead to damage.