I can’t comment on sound quality differences between CDX2 and ND5XS2 as I haven’t compared - and you are quite capable of that anyway.
However with streaming from your own store vs CD, streaming has the potential to be better quality, because it does not have the removeable physical disk that can get damaged or dirty, causing read errors, and so does not need error correction algorithms, and because it opens the door to higher resolution recordings (higher bitrate and/or greater bit depth). There is also the convenience factor, no more finding and changing disks, all possible from a remote control and the comfort of your seat. (Don’t worry about a dedicated remote control, there is an app that runs on a smartphone or tablet that does far more, including enabling you to see album art.) And you can do away with all the CD storage space, at least in your listening room (for copyright reasons, if you have ripped CDs as opposed to bought downloads, you cannot sell or pass the CD to anyone else, and keeping it is your evidence of source). Some people also like to play individual tracks, rather than albums, and it lends itself well to that, including building of ‘playlists’ if you want. And you can make a backup (or multiples) of your entire collection on a separate hard disk, which if stored somewhere else can give you a very robust recovery ability in the event of disaster.
Ripping is easy if you have a computer with a CD drive. Many people use a program called dBPoweramp, which will campare your rip with online an online database to check for accuracy, and advise if any evident errors - when that program has various intensities (speeds) of ripping to try to cope with the most difficult of disks. (When I ripped my collection well over 90% ripped with no difficulty whatsoever at the default, fast, setting.) I’ve had a very small number of CDs (single figures) where the Rio has shown a track hasn’t ripped accurately, but still sounds OK - and that undoubtedly means a fault on the CD that would have been no better playing durect in a CD player - and quite a few where the ripping had to be intensive to get accurate: which playing direct may simply have killed in error correction interpolations, or created audible gaps or stuttering etc. And once ripped, no such problems ever again! Many people streaming-only still buy CDs, including secondhand, for ripping. Otherwise buy by internet download.
Streamers also open the door to online streaming services, the better sound quality ones available by paid subscription. Some people use those universally instead of their own stored collection, others mix the two, others only use free online services even if lower quality, as a means of hearing new music to decide whether to buy. Pros and cons, but that is for another time. There is also internet radio.
I switched to streaming several years ago when my CD player was dying, and have never looked back - it is so much better overall, with the only negative being that the CD artwork/insert needs viewing on a screen not physical - and to do that you need to scan it, or hope to find that there is an online version. With operas having librettos, as a CD “jewel-case” sized booklet, I have kept the CDs in the music room.
There is one important detail of which you need to be aware before starting ripping and downloading, which is that streamers use embedded ‘metadata’ in the music files to identify and browse/search for music. CDs usually have that already, which is copied with the music rip, likewise downloads, however it is not always complete, nor is it always consistent in the information it contains, and as it can be critical for ease of finding music in your collection you should always check it for consistency, completeness and accurately after ripping - and get in the habit of doing that from day 1, as once you have a few hundred album with metadata missing or wrong it becomes a real pain to fix.