not sure the technical details of how roon communicates with connected devices. however, the dac8 dsd is a roon tested device. according to roon:
Roon Tested devices from our partners have been profiled and tested by both Roon Labs and the device manufacturer for maximum compatibility.
Roon will recognize these devices and send them audio optimized for their capabilities.
before doing the amanero USB receiver firmware update, the max dsd sample rate shown by roon was dsd128 via DoP – this is 100% consistent with the info in the dac8 dsd user manual.
after updating the amanero USB receiver firmware to CPLD_for_1081 and 2006be11, native dsd playback is enabled and dsd512 is shown.
so, this leads me to believe that roon is dynamically detecting the USB capabilities from the dac (based upon the installed firmware).
here is a screenshot of how i configured sample rate conversion:
how are you currently connecting the dac8 dsd?