Same problem here: from the new update, season 7, the 7.1 audio doesn't work anymore.
The only way to make the game playable is to set the game in stereo mode.
Acting in the config file, located in C:\Users\[username]\Saved Games\Respawn\Apex\local\settings.cfg
(Open this file in notepad)
changing the line that says "sound_num_speakers"
as following:
7.1 is value "8"
Stereo is value "2"
seems not work on windows 10, only respawn knows why. (but i set it correcly anyway)
Works properly instead, this way: go to
Origin > My game library > right click on Apex > Game options > command line options > add +miles_channels 2
this command set properly the number of speakers, 8 for 7.1, and 2 for stereo.
Remember to turn off the virtual sorround (spatial sound) from the windows setting, in your windows speaker audio properties.
i used to hear better than anyone, with my real 7.1 asus rog strix headset and audio was one of the most perfect things in apex legends.
Now is ruined, i really hope respawn will fix this.