@jon_5912 Stereophile measured the CS3.7 impedance as low as 2.2 Ohm, so even the more powerful AX-5 might be a marginal match for big rooms or loud-preferring listeners. Still, I'm surprised the AX-7 didn't at least deliver good sound at moderate SPLs.
Wes Phillips used several amps for his CS2.4 testing including a vintage Fisher measured at 6W into 4 Ohm!
. . . while not my first choice for the job, did not acquit itself too badly.
But for his review of the CS3.7 he used the Ayre MX-R and Musical Fidelity Nu Vista (480w into 4 Ohm).