If Gryphon recommends it then I’d lean that way. But, I would try it both ways and find out.
I used to follow the rule of plugging my main amps into the wall. Just recently I decided to try it running them into my power conditioner. I think it definitely sounds better through the PC. I'm not switching back. (I had already been running my sub amps into the PC.)
I also read the manuals of my PC and main amps and it didn’t say anything about it. The PC basically said plug whatever you want into it.
For reference I have Pass mono blocks and a Running Springs Dmitri.
I’m very curious about the Audioquest Niagra 7000. And because it’s designed to allow you to plug your amps into it, this is one reason I tried it with my set up.