The question I usually always ask is why anyone would use Direct/Pure direct though? This means no bass management, which means no subwoofers which means you could just as well buy a dedicated 2 channel preamp instead. Also you're missing out on room correction and so on. It is not worth the effort to try and run a Pure Direct setup with an AVR imo. Unless that is that you have an external crossover filter and doing a very advanced setup and need no room correction due to rebuilt room etc. But then again with kind of money buy a state of the art 2 channel preamp+DAC combo instead.
I have tried Pure Direct on a Marantz unit with surround during a demo scene with 10Hz content (this was years ago) without quite knowing what pure direct does. And at least in my unit the center channel 9" woofer was going crazy so for sure no bass management activated there. That was the last time using it. Imo at least no speaker is big enough to run full range. Always off-load to subs for less distorsion from speakers.
Agreed, aside from the use of subs and bass management, I can't hear a difference anyway. However, I would bet someone like RichB could, and unless we are there with him in a DBT session, we would have to take his word for it that he could in fact tell a difference. He can even hear a difference between his AHB2 and AT400NC (only iirc)