Upsampling - but seriously folks

no problem phil9624. :-)

but actually downsampled some 192/24 FLAC Neil Young albums from PONO to 96/24 WAV and think it sounds better, also smaller file. Go figure! Best, Phil

it's not entirely surprising. As you know, the fold-over frequency for 192K is 96K & your digital stream is incoming at 192K. The circuits involved in handling this digital stream & the corresponding analog circuits need to have 2X the bandwidth (compared to a 24/96 data stream). So, the real question is: in your electronics, were the circuits designed for higher bandwidth? If not, it is quite possible that the circuits are distorting & even tho' the 24/192 might be cleaner/better sonically, the circuits are unable to render this correctly.
Dan Lavry (manuf of Lavry DACs. Lavry DACs are well regarded in the audiophile world) wrote a pretty nice white paper on this:

http://www.lavryengineering.com/pdfs/lavry-white-paper-the_optimal_sample_rate_for_quality_audio.pdf

and here is another white paper on Sampling Theory (which i think you know well w/ your Physics degree) which touches upon the pros & cons of 192KHz upsampling:

http://lavryengineering.com/pdfs/lavry-sampling-theory.pdf

It seems pretty simple - try it and see what you think. On some systems it helps, on some systems it hurts and on some system there is not difference. People can write all they want about the theory of this, it all comes down to the implementation of the upsampling and the implementation of the DAC and other components. There is no answer - other than to try it and see how it works for you.

dtc, 

That is very well said. 

J. :)

The technology is always worth knowing and understanding but in this case I would just listen and compare.   Either way can be done well or not.   What any individual will prefer soundwise cannot be predicted.

FWIW I have both oversampling and non oversampling DACs in that the technology interests me to compare, and I find each sounds much different but very good in its own way.   Lots of good flavors of good quality sound out there.