I've read through this thread and just had to jump in
The advice you've received is sound, pun? and PiCorePlayer is an excellent low energy solution but my only gripe is the price of Pi-s
The price is beginning to fall but you might be better served by an older HP 1L server or a newer minipc
For around $150, you can get a nice low energy solution that could run Daphile, be able to expand the storage more easily and reindex the files much more quickly
Also be usable as a file share so you can move backups in or out of it
My advice is a $150-$200 minipc and Daphile OS plus plugins
Daphile is an audiophile class music server & player OS – targeted to dedicated headless PC. It manages the bitperfect and gapless playback of common audio formats including the high resolution files.
daphile.com