No he didn't say that, he just said disconnect. In fact, he had previously said Denon's preamp mode (dated back to the older models such as the X7200W and 4520) were not truly preamp mode because the power amp sections were still powered. As far as I know, no AVRs have the power disconnect feature. In the Y-tube video he even asked the Denon reps if in this so called preamp mode for the 2020 models, would automatically switch ECO to "ON', in order to run cooler by lowering the rail voltage, implying power is still on.
Regardless, in terms of audio performance it should not matter because if you look at the ASR measurements, the reviewer (Amir) have already verified that even just by disconnecting the pre-outs to the power amp inputs, the AVR-X3600H measured just a touch below the $4999 Emotiva prepro but better than the Marantz AV7705 and TLSGuy seems to like. In fact, the Denon AVR also measured better than the Marantz current AVP flagship AV8805. The Marantz are real AVPs, i.e. without power amps, so we should be able to logically assume while disconnecting the power supply completely to the power amp section must be better in theory, it may not make any measurable difference.
Note that in the chart below, at slightly below reference level, -0.5 volume position, the Denon's SINAD actually exceeded the
$5,000 Emotiva RMC-1's 100 SINAD.
Amir noted: If you reduce the output to 1.4 volts, SINAD of the center channel improves to 97 dB whereas the Left goes up to 103 dB. This is at volume position 79.5 dB (above is at 82.5).
The 103 was obviously a typo, if you look at the display it was 100.352 dB, but that's less than 0.001 % THD+N.
That's when he was asked to compare with and without power amp disconnected, so he set it up to compare the left and the center channel. The AVR-X3600H can only disconnect the front left and right channel. I know this sounds confusing but I hope it is clear enough for you.
That's THD+N of only 0.00096%
ASR review - with power amp disconnected vs connected
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