David, I am using Wave Editor and routinely upsample 16/44.1 files, first 16->24 bit, then 44.1->88.2 kHz (relative order matters here). I prefer the sound of these upsampled 24/88.1 kHz files, it appears smoother, more liquid, but the difference is not dramatic. I am using Amarra 2.32, Audiophilleo2 and Metrum Octave.