Never heard of Ulilith, interesting concept (the play from memory).
RE: Plex, I tried that for about an hour and quickly uninstalled it. Not only did it transcode files but there were latency issues as well. Junk IMHO.
Plex supports lossless audio it will not transcode, but you will need to set up a setting for it.
I couldn't figure out how to not make it transcode. I did play around with the settings. From everything I was reading online, the software transcodes (sounded like it too). Even if I could solve that the latency issues were a dealbreaker for me.
My chain was this:
Windows 10 PC > WIFI > PS4 > Toslink > DAC > Integrated Amp
Honestly it was such a PITA I'm not going to bother trying it again. At some point when I can afford it, I will set up a NAS and a dedicated music PC or DAC/Network streamer device. Not exactly cheap so that's why I haven't done it yet.
For now it is simply easier to run Foobar on a secondary laptop, then output USB to DAC. That or just play physical media.