The Steely Dan - Aja, Japanese SHM-SACD released in 2010 sounds absolutely incredible!

I torrent my files, then play them back over my stereo via a RaspPi running Volumio

Did you not just answer your own question? If you’re concerned about replacing the ‘perfect FLAC’, I would assume you would download the 24-48 FLAC files.

Also, unless you know the music was recorded at 16-44.1 I wouldn’t assume that the 24-48 is upsampled. A lot of music is recorded at higher bit rates and then put out at lower. So your 16-44.1 may actually be downsampled from the 24-48 or some higher rate. Not saying upsampling doesn’t happen, it’s just my thought on the matter.