This is from the Pontus 2 spec list on the Denafrips page. I have no reason to doubt what Alvin passed on to jjSS49, so beware there.
DSD
DSD64 (DoP) on Coax/AES/Opt Input
DSD1024* On USB & I²S Input Only
PCM
24bits / 44.1, 48, 88.2, 96, 176.4, 192KHz On All Input
1536kHz* On USB & I²S Input
Clearly,
Denafrips has put a great deal of effort into their USB and I2S inputs
as they probably reasonably expect those to be the most commonly used.
As have Antipodes with the USB output on their line of server/streamers of which I'm a very happy owner.
I have the S30 and use Roon with a Curious Cables USB cable into my Pontus and it sounds fantastic to me when streaming Redbook and higher.
I'm considering trying one of the Denafrips reclockers to use the I2s input as their DACs respond very positively to that input by all accounts.