Uncompressed 2ch 44.1kHz 16bit PCM is only 1.4Mbps. Even 7.1ch 96khz 24bit is only 18.4Mbps. Should be plenty of headroom even on "only" 100Mbps.

If you are referring to in-network, I've never had issues with FLAC files up to 24/192. Out of network, I use Plex and PlexAmp which can encode the same files to OGG for more mobile friendly streamging

That's on my list of things to find out! I believe the Pi I'm using (the Model 3B) only supports 10/100 Ethernet, so bandwidth might be a concern. From a quick search plenty of other people are using Pis (including via HiFiBerryOS) as FLAC players, so that part shouldn't be an issue.