The current state of the art is class D with DSP. A top notch film screening room that supports Dolby Atmos will use a stack of Crown DriveCore XLS series amps in the rack (not the better CDi series because those are way more expensive, and if you have a reasonable Atmos installation of 30-some speakers, the costs add up.) Anyway, the XLS series lists THD as <0.5% at rated power (CDi is 0.35%). IMD (60Hz and 7kHz at 4:1) from full rated output to -30dB is listed at <0.3%. By these measures, the extremists would consider them a fail. Again, we are not talking about a local theater that sounds pretty good, we are talking about the top mix stages in Hollywood.