Hopefully the right thread here for this. After being pretty fine with “little” chain, would like to tune my “big” chain a bit too. So, this is Gustard U12 - Gustard X12 (via I2S) - Sennheiser HDVD 800 (fed via balanced XLR) When using a PI 4 with NAA to feed Gustard U12 via USB I am able to do DSD256x48. Which is pretty fine already. Not sure if DSD512x48 would be of so much benefit. By using U12 hope to pretty much escape USB disadvantages. Going via Tos or Coax would be possible too, but then no DSD256 anymore 
++ Anyway, the Pi4 Solution right now already sounds pretty fine imo. But I am thinking of getting an ifi Zen stream for NAA and others stuff and would feed U12 via USB form ifi. Alternative would be to get an i2S output hat for the Pi to feed the X12 DAC (or following DAC i might buy in future). So dropping the U12. Candidates for i2S output from Pi IAN CANADA FIFOPI Q3 ULTIMATE FIFO Reclocker Module PCM 32bit 768kHz DSD1024 DoP - Audiophonics and IAN CANADA HDMIpi MKII Transmitter I2S / DSD / DoP to HDMI - Audiophonics ++ not sure if this i2s hat combi would work at all with NAA?? ++ This is all pretty in the beginning. But any remarks from you folks highly appreciated 
(@Nigel_Potter - just if you have time and like to )
++Edit: This one looks interesting too for my constellation… USBridge Sig - Ultra low noise RPI // Allo USBridge Signature review | Darko.Audio
And another one, Here mentioned to be compatible with i2s Gustard… PI2AES - PRO AUDIO SHIELD
Yep, I think it is done Will be PI2AES. Take a look here too please: Simplify my HQP NAA + Mac mini + Pi4 RoPieeeXL + Pi2AES runs? - #11 by Michael_Pauliks
Maybe will wait for this one: Coming Soon - Pi2 Design
Thank you all, have a nice weekend and enjoy the music