You've properly also directed this qn to the April Music site. If you already own both, no harm in trying it, and I suspect that the Stello might be able to conform its output to 24/96. Interesting experiment to see how an asynchronous USB-S/PDIF converter will match up with a DAC that uses highly refined isosynchronous filters.
If you haven't purchased yet, it's probably worth waiting for the mfr's response, or also consider one of the Bel Canto USB converters designed for the DAC3.
If you haven't purchased yet, it's probably worth waiting for the mfr's response, or also consider one of the Bel Canto USB converters designed for the DAC3.