my opinion is that to surpass widely accessible streaming file sources for most vinyl you will need superior level vinyl playback as well as a high quality adc. looking at your system such an adc device such as the Merging Technologies Horus will exceed the cost of your entire system. if you go for a more modest level adc your result will be compromised and likely you will find on line sources with equal or more likely better results for performance for your Mercury’s and RCA’s. even the direct to discs have some files although they are vinyl based.
and most old Mercury and RCA recordings have very fine digital tape transfers; the RCA's have great dsd files from tape that can be downloaded or SACD's that can be purchased.
https://www.merging.com/products/interfaces/horus
so my view is the solution is streaming, not ripping to dsd256. as the result will not be the best use of your assets.
i have over 1000 vinyl ripped dsd128 files done on a Merging Technology adc while they are very nice sounding, mostly i prefer streaming files. which are tape based, not vinyl based.
YMMV.