The sound technology behind WC3 is probably very primitive by todays standards. Today all Windows operating systems since Vista force resampling of all audio channels from applications to a standard output rate and precision (configurable per adapter) and then mixes them together to produce the audio out, solving mixing, audio device sharing and driver stability problems which were notoriously a problem with sound drivers.
This was not the case back when WC3 was made where the game needed to use a third party library to manage sound driver interfacing which might have imposed other restrictions or requirements. As such WC3 might have very fixed bitrate and sample rate requirements as it might not be able to mix them together under certain circumstances.
When replacing in game music files with custom imported music files be aware that the bitrate and sample rate are determined by the slk entry for the music. If it does not match those of the track being replaced WC3 will fail to play it at all.
