your setting, is a global setting for all sounds.
so you need another way.
If you want to play AM Intro Video with sound + disable sound for snaps, you need to edit the display/layout code itself.
SeeGoto display folder:
Your-AM-folder > layouts > your_layout > edit layout.nut
search for this parameter:
snap.preserve_aspect_ratio
add this extra code line just below:
snap.video_flags = Vid.NoAudio;
So you get:
snap.preserve_aspect_ratio = whatever;
snap.video_flags = Vid.NoAudio;