Right, so it seems that some of the instruments are getting virtualized due to the VOL0 Virtual feature. Lowering their volume to -79.9dB instead of completely muting them solves the issue, however that leaves the tracks slightly audible when they should be completely muted.
As I understand, in order to disable this feature, I’d have to change the FMOD_INIT_VOL0_BECOMES_VIRTUAL flag. But according to this post it is impossible to change the init flags of the Unity integration.
Are there any alternative ways of globally preventing sounds from getting virtualized?