In order for plugins to play sounds on client machines,
res files must be specified.  A res file is a simple text
file that tells a client, on connection, what to download
from the server.  For custom sounds to be player on a client,
a res file must specify that those sounds be downloaded
to the client.

Res files are on a per map basis and have the name of the map
as their name (except res files have a .res extension).
If you wanted to create a res file for de_dust, name it
de_dust.res

When clients connect and your server is playing de_dust,
they will download anything specified in de_dust.res
that they do not already have.

If you want clients to download soudns for every map,
then you need to have a res file for _every_ map.
There is no way to get around this so don't bother
asking.

Res files should be placed in the "maps" directory of
your mod.

The contents of a res file are simple declarations of
where files exist on the server that the client should
download. These files are specified relative to the
mod directory.

EX:
sound/misc/multikill.wav
sound/misc/ultrakill.wav
sound/misc/killingspree.wav