From what i know/remember the voice chat commands in e+ are played from the client's PC.
The server can have different wav files but then the clients must have the same files too.

You can see on this likn the The wav files and how to use them
https://www.excessiveplus.net/documentation/client/communication

I'm not sure if this is possible.. if i remember correctly you can:
add a pk3 file with all new wav files you want to use.
The clients must download the pk3 file when they connect to your server. By having
sv_allowDownload 1 in your server config the pk3 will be auto-downloaded when the client connects to the server.

if the e+ doesn't use a specific list of wav files:
You could add any wav file in the pk3 and play it like say "&<wavfilename.wav>"
Otherwise it means you are limited to use only the existent filenames (see the communication link above)
This means you can add the waves you want but use the same filenames. The new wav files will overwrite the old ones if the pk3 file is read after the original one. You can control this by having the pk3 file named like "zzzz_last_file_ever.pk3'

From the communication page i understand that it might not work with other files:

E+ doesn't have open source code so i don't know how is this implemented. But with trial and error i think you can achieve a way to do it.
You can try rcon "say &gen_movepls.wav" but since "say" is a client command it will be executed on client side and read the wav file from the client's pc not the server's.
If the server has the file but the client doesn't it won't play anything.

In the same way it works on quake live probably. The wav files (in a pk3 file) must've been downloaded on server connection. The client plays the wav file from his wave pk3.

Other way to do it is by using the "play command"

play
(command)

Plays a .WAV file in the current game directory one time.

But this command is executed on the client too => the client must have the wav file.

If i said smth wrong please correct me.. anyone!
__________
epsislow