Taking a relatively low resolution signal such as Redbook audio and carefully interpolating samples between the existing samples to increase the effective resolution is the kind of “distortion” I can get behind. I imagine a crude drawing on graph paper with medium sized blocks transposed onto another piece of graph paper with much smaller blocks.
44.1/16-bit is in no way “low resolution.” It 100% perfectly represents a signal up to half the sampling rate. Meaning that the EXACT same original analog signal can be recreated from the digital data within the bandwidth limits. That is a mathematical fact. See the Nyquist–Shannon sampling theorem (wiki it). If up-sampling is improving the sound, it is not because of curve smoothing (“medium sized blocks transposed onto another piece of graph paper with much smaller blocks”). The idea that curve smoothing is needed is based on some poor technical explanations of digital signal theory and on deceptive marketing. The graph paper plots of the digital data are a gross simplification to make complex digital theory more understandable. In reality, it is not a jagged curve unless that was the original signal. Any sound difference is most likely due to how your DAC handles the up-sampled data.Its filter may work better with 192K (for example) than with 44.1. It is arguable if this is audible, but there may be cases where it is.