The users on this board have determined that Netpliance sold i-openers with about six or seven combinations of chips and other features.
The i-o considered as version 5 came from the factory with a cpu made by RISE, a Trident Display controller, a VIA 82C686 'South Bridge' controller and Analog Devices AD1881 sound chip. The AD1881 is straight above the keyboard connector.
If your i-o has an AMD cpu that you did not install, someone has been inside your i-o before you. If that is so, do you know who you got the i-o from and if they tried to modify anything else other than change the cpu?
If the previous owner tried to connect to the sound circuits and failed, that could explain why the sound does not work. If that is what has been done, you may not get the sound to work.
If you know who you got the i-o from, ask them if they attempted to connect to the sound.