Simple solution but it works: the internal 1TB drive that Apple's contractor packed into our Mac mini, with a network backup. The internal drive is only used for storage. The OS and software run on an external Thunderbolt interface SSD. Compared to opening up the machine and changing the internal drive the external drive was more expensive in parts. Adding in my billable rate it ended up being much cheaper to buy than build.
All of our stored music is 2-channel Apple Lossless, except for a few things my wife bought on iTunes, so 1TB is adequate. I haven't figured out how to burn SACD and DVD-A, nor is it clear to me that there's a no-fuss playback system. So multichannel is still played on disks.