The only way to get DSD256 to a capable McIntosh DAC is via a Windows computer and the McIntosh provided Windows ASIO driver.
But be warned when using Native DSD mode with the McIntosh windows driver you will get pops on start and stop of playback with Roon and HQPlayer. McIntosh is aware of the issue and choses to do nothing about it as Native mode is only really specifically needed for DSD 256. DOP will work fine up to DSD128 as you have discovered. I was told via emails from McIntosh that there isn’t much DSD256 content anyway and then told the files are too large anyway, I was also told that hitting double pause in the JRiver was the right way to handle the POP from Native DSD. At that point I lost my cool. Now a half year later Ron doesn’t remember the conversation and publicly called me sad on AudioKarma.
Apparently on the expensive D1100 DAC/Preamp they’ve implemented a very short fade in and out via a firmware update to vastly reduce the loudness of the pop.