The sound files are .WAV in "16-bit 16kHz PCM" format.
16kHz is not a supported format. Please see: http://www.voiceguid.../soundfiles.htm
As this is a G711 VoIP based system then the best format to use would most likely be "8-bit 8kHz ULaw" format. "8-bit 8kHz ULaw" format is what is transmitted on most VoIP/SIP connections. So if your sound files are recorded in "8-bit 8kHz ULaw" then the sound data bytes from your sound file will be the actual bytes transmitted over the SIP connection - giving you exact control over sound transmitted to caller.
Please ask the source that provided these sound files to supply the sound files in the .WAV "8-bit 8kHz ULaw" format.
In the meantime please see attached. That .ZIP contains your sound files converted to "16-bit 8kHz PCM" format.
These sound files will work with VoiceGuide, but as they are converted from your 16kHz files they will not sound as good as the ULaw sound files generated from original high quality recordings.
If you arrange to have sound files provided to you in .WAV "8-bit 8kHz ULaw" format from the original source then this will result in best sound quality.
(You can use WireShark http://www.wireshark.org to confirm what is the actual sound encoding format used on your SIP connection)