I know THD+N is not a good indicator of sound quality so please do not tell me again. Just for fun though, I found the following THD+N specs of some not too expensive power amps:
Anthem P2: 325/500WPC/8/4 ohms: continuous RMS, 20 Hz to 20 kHz, <0.1% THD, one or all channels driven.
ATI: <0.03%
Bryston: ≤0.005% Full bandwidth, at rated output, all channel driven.
Krell Duo 300 XD: <0.045% at 1 kHz, at 400 W, 8 Ω, <0.17% at 20 kHz, at 400 W, 8 Ω
Passlab class AB XA series: 1% at 1 kHz, full power
McIntosh monoblocks: 0.005%
Classe CA-2300: <0.002% at 1 kHz balanced, <0.004% at 1 kHz single ended
Parasound Halo JC-1: 0.15% at rated output
Expensive ones:
Boulder 3060: 0.003% full bandwidth, rated output
Goldmund Telos 5000: 0.0005% full bandwidth, rated output (presumably, for a million dollar welder
)
So far I couldn't find anything with better THD+N specs than the ABH2:
< 0.0003 % THD+N at full rated power, 20 Hz to 20 kHz
The second best appear to be Bryston and McIntosh SS amps, based on specs, not bench tests.