Many thanks to goldsdad for the explanation!
With the Musical Fidelity V-Link Mk2, I found that all music sounded so much better - cleaner and with more impact. I was thinking that, whether the DAC was "stuck at 48kHz" or not, something must be working right. Anyhow, I purchased the Mapleshape / M2Tech USB-to-S/PDIF converter also to try. It sounded as good, if not better.
Now I know what's going on. My system is sounding good, but I will pursue a firmware upgrade for my i3.3.
Does this status bits issue explain the "48kHz" problem of the Simaudio 300d (when used with the V-Link) in the original thread?