Thanks Alp.
Stan is about to send to me one of his latest batch of his latest DAC. My 7510 is close to 20 years old!
Experts on https://forums.slimdevices.com/ offer the opinion that whereas the USB output from a Pi3 could be rough that from the Pi4 is extremely good.
Time will tell. Maybe Stan has some comments even now.
Brian
In Southampton: Raspberry Pi 4 running PiCorePlayer, Beresford Caiman SEG, Quad 77 Int Amp and CD Player, AVI Neutron 4, Sennheiser HD25 headphones.
In Nicosia: Small Format HTPC, Beresford 7520 ,Quad 405-2, Quart 980s German Tower Loudspeakers.