It was basically Borealis music at night. After a few years, PC upgrades and ISP improvements made it impossible to hear before AO loaded.
The music files reside in the main data directory for the game itself - with most in a readable (.wav file) format. (Funcom\Anarchy Online\cd_image\sound). The music directory (music\env ) would be my best guess to start.
I also think there was a CD made at one time with all the ambient music for an anniversary or promotional of some sort.
I found my copy of the CD, it has 14 tracks on it, I also found a link to this collection on Spotify which seems to have a few different ones:
But it also seems to be a dead playlist.
Thanks much for the responses.