To answer the original question, the point of upsampling is when you put, say, 48kz material into a DAC at 48kz, you get a cascade of reflected images at higher frequencies of the recorded material theoretically forever. Some don't worry about it, and you have what is called a NOS DAC that some like. But since the frequencies go on forever, it can cause problems with amps, etc. So what you do is upsample it. A straightforward process is duplicating the samples to get 96k, 196k, etc. It is called 2, 4,.... etc oversampling. Eight times, oversampling is common. Then, those cascaded copies of the signal occur at a much higher frequency that is easy to filter without affecting the audible band. DACs often do that for you. However, some believe a better quality filter (technically with many taps) affects the sound quality. Rob Watts is a proponent of that with his M-Scaler; there are plenty of reviews on the device, and Rob has videos on it and how he designs DACS. First, how he designs DACs with massive upsampling:
Then, on the M-Scaler:
I like the M-Scaler, but others, some even more experienced Audiophiles than me, don't.
I know a DAC designer who solved the issue elegantly. He uses a standard DAC chip and the best quality Sowter Audio Transformer he can buy as output. That is virtually flat to about 70KHz and rolls off rather steeply after that, preventing any high-frequency stuff from being output. I have compared his DAC to much more expensive DACs like the Direct Stream, and IMHO, it is better. It is not better than a Chord TT2, but that is MUCH more expensive and not better than the even more costly Grandinote DAC - but they are the only two better DACs I have found.
Of course, better here means to my ears sounds better - if it is better, it depends on what you mean by better.
Thanks
Bill