FYI, there was just a huge update to the available FF soundtracks on the big streaming services. That includes all of the FFXI main+expansion soundtracks:
FFXI OST (original game)
Rise of the Zilart
Chains of Promathia
Treasures of Aht Urghan
Wings of the Goddess
Seekers of Adoulin
FFXI OST Plus (mini-expansions, Abyssea, POL music)
Forever Today (additional Seekers of Adoulin era music)
Doesn't include some offshoot/compilation/arranged albums like the Sword Songs album (battle music compilation), Nanaa Mihgos or Star Onions albums, Piano Collections, etc. But there's a TON of stuff on there now.
Also lots of other FF series soundtracks added:
- All of FFI to FFXV (including all of the main FFXIV OSTs)
- FF Tactics
- XIII-2 and Lightning Returns
- Kingsglaive FFXV
- Dissidia/Dissidia Duodecim
- FF Type-0 HD
- Crisis Core
- Record Keeper
- Several "Plus" or special/arranged albums from the main series games
At least on Apple Music, search can be kind of messy, but they're all in there. You get a lot of the results by searching "Final Fantasy Original Soundtrack"
Also of interest, Apple Music has had Distant Worlds vol. 1-4 for some time, and vol. 5 showed up in this new batch of additions (not sure about Spotify availability). Excellent stuff, with some FFXI tracks included.