Excellent, thanks! I did not know these products.
The second one that you have linked is even rather cheap, and seems to
fit well my needs (as I said, I'm not interested in the DAC part, but
only in the optical out)
scala'
I can confirm that the HiFiMe products work with piCorePlayer although
you may need to increase the output level via alsamixer.
https://hifimediy.com/product/sabre-9018-uae23hd-usb-dac/
https://hifimediy.com/product/sabre-dac-uae23/
The 3.5mm output is optical as well as standard jack.
They a