Well, the project is almost completed, the setup works (althought I had to reinstall DietPI on the microSD, as if the NanoPI did no longer want to boot correctly).
The network switch is not yet plugged on my new home made power block (3 outputs, 12V, 10V, 7V) and there’s still few things to arrange but the most important is there. The NanoPI and the Hecate board are now powered by the small LT3045 regulator (5V/1A) and the AudioGD HDMI module by an independant regulation line with a smaller LT3045 regulator (3.3V/500mA). I had to say that these regulators cards seems well built (bought on ebay @ lvdor).
Now, the SOUND 
For few weeks ago, I already used the combo (Armature Hecate + AudioGD HDMI + either the NanoPI or a RPI3 SBC) with Roon bridge and Dietpi. I tried also Ropieee which permits to stay in native DSD (not DoP) between the SBC and the Hecate board. The Hecate boards always output in Native DSD (when DSD is presented in input) up to DSD128 (limited by the Directstreal actualy). The whole was powered by one small linear 5V PSU and a small 3.3V regulator (LM317) with a 6V battery. I already found the sound quality very good on this setup.
I only had a relatively short listening, but the new power lines brings more clarity and details. I would say a also gain in soundstage. I’ll let pass the satisfaction to be at the end of a long work to not interfere on my judgement on the SQ, but it is obvious that it works better than before
