.dff is the DSD format of the original recording in the case of Channel Classics. .dsf is .dff with tagging added. What's preferred depends upon what's important to you. You can easily convert a .dff format file to a .dsf using AudioGate. It takes just a second (literally) for just the extension name is being changed, and some blocks for tagging data tacked on. No content data is changed. Your JRiver media Center is the ideal Tag editing tool to then add whatever metadata you want.