In my unit it's not working like that. If I2S is used, turning on USB doesn't switch it to USB until I2S is off.I think USB input takes priority,
No debate is necessary as it's easy just to try. I got Ricable Dedalus 0,5m. At this point I can't say which input may be best for me: I2S from Gustard U18 or USB directly from Daphile.If you ask me personally the Excalibur improved clarity a little bit in my system when I bought it a few years ago, but I have no intention opening a debate with my post.
I2S in this config sound is more airy (like it's brighter), it feels there's more resolution because of it.
USB has more "meat".
Choice between generic USB cable and I2S was simple favoring the second, so to my ears premium-ish USB cable does something better.
Concluding,
this forum made doubt in any common sense opinion I had on things that should not make any difference to sound from any device, like fuse. Boy, how disappointed I was after putting SR Purple fuse to Pegasus DAC, cause common sense failed.
Now USB cable..