Thanks for the clarification. It confirms that I’m doing the right thing. I’ve already been setting up all my mastering sessions at 64/96 (for mixes given to me at 24/48) or 64/88.2 (for mixes given to me at 24 / 44.1). I use Lynx Hilo A/D D/A.
I sculpt the sound with plugins and outboard analogue equipment. The upsampling in Studio One 6 is excellent. Here’s an interesting resource I found for comparing software sampling rate converters.