I have never seen a comprehensive explanation of its effect. I do remember back in the early days of upsampling ( around the turn of the century) dCS published a white paper about the difference between upsampling and oversampling. This was really a consideration of a conceptual or mathematical nature. Where the paper dealt with subjective aspects if I recall correctly ( and I may not), it concluded along the lines of “There’s something going on but we don’t know what it is”.
Of course upsampling does not add any additional information about the music. The music information is the same in a native 16/44.1 file as in a 24/176.4 file upsampled from it. So something else is happening. It may be that there is a benefit from the fact that upsampling places the digital filter further out of the audio band. That is only speculation on my part.
I have found certain abberations to occur when upsampling, the subjective nature of which can be found in my past posts on this forum so I will not rehearse them now. Note I am referring to the process of sample rate conversion as selected by the dCS user from the options offered rather than to the form of data “conditioning” that is part and parcel of the way Ring DAC works.