Are you saying you prefer the DXD files upsampled by your server to DSD 256 to the original DSD 256 of Challenge Classics?
On my Tidal La Assoluta/Kondo system I prefer the original dxd recordings of Challenge Classics to the dsd 256 files they make from their original dxd recordings. Although the dsd 256 files are somewhat softer sounding and from a tonality point of view more beautiful sounding, the dxd files are sounding more open and dynamic. And the tonality of the orginal dxd recordings of Challenge Classics is beautiful as well, although maybe a tad less refined. At the moment I let the Golden Gate 'upsample' everything to dsd 256 and it is this mode that I prefer the dxd files. Have not yet tried to play the Challenge Classics dxd recordings with the Golden Gate dac in pcm mode (my Lampi can do this if I want).
I am very fond of (good) original dsd recordings as well because I like their smoothness and liquidity that resembles somewhat vinyl replay. However, good pcm recordings can be extremely good as well as the original dxd Challenge Classics recordings show. For me the latter belong to the very best classical files that are available today, although I must add that I am very impressed as well by the original dsd 256 Eudora recording of guitar music by Fernando Sor. But recording a single instrument is of course much easier than recording a full orchestra as Challenge Classics is doing.
Please keep in mind that I am particularly referring to the Challenge Classics recordings that are being engineered by Bert van der Wolf and are being made available through his spiritofturtle website. Challenge classics records also with other engineers; these recordings are sometimes available in sacd. Bert van der Wolf older Turtle recordings are very good sounding as well. Some of these recordings are also available on his spiritofturtle website, albeit that these recordings are most of the time original dsd 64 recordings; these recordings are not available in dxd format.