Tricky one this, but I would suggest that digital signalling technology is sufficiently robust as to deliver a “bit perfect” digital data stream from the transport (CD drive or digital streamer) to the D2A converter circuits, whether those circuits are integral to a CDP, or external to a “stand alone” DAC.
Is that is established, then the quality of the analogue signal presented to the preamp would be largely dependent on the quality of the D2A converter circuits, whether those circuits are integral to a CDP, or external to a “stand alone” DAC.
A cd is a transfer mechanism for me. I do purchase FLAC downloads from Bandcamp and the like but it doesn’t “feel” the same. Which all goes to show that I am a dinosaur.
Re sound quality, if all else is equal, including the same DAC, then still streaming from your own stored oil ripped from CD has the potential to sound better because it eliminates The read errors can occur with us to 40 or dirty discs, mechanism going out of alignment, et cetera – no jumps or starters, and no interpolation by Eric correction algorithms.
That said, some people find that when they are streaming from their own store across a network, other influences can have a negative effect on sound quality (e.g. due to RF noise picked up or transmitted via the network, so that in turn network cables and switches in such instances can affect the sound. However that very much depends on their network set up, electrical environment, and most particularly depends on the renderer and DAC concerned and how well isolated they are.
I switched from CD to streaming from my own store 6 1/2 years ago now, and have never looked back. Aside from the many convenience factors, I certainly do not miss the occasional miss reading of CDs, and the need for replacement of one CD mechanism or the whole player every 10 years or so. However in my set up I do not stream across the network but the music store is in the same machine that renders them into the digital music stream reading directly into my DAC.
I still buy CDs, E.g. when only available in that medium, or (surprisingly) CD is cheaper than same files available by download, Wall buying secondhand. I immediately rip to FLAC.