try another HDMI cable and if you have another source of hdmi signal try it. When I connect my encoder box to the computer, the audio line in System status shows audio informations, if I disconnect HDMI cable these informations disappear.
It is possible that audio does not come throught your cable or audio is not present in your hdmi connector - wrong setup of audio output on your computer.
It is also possible to test your computer HDMI output with TV to check if audio is present.
If audio is flowing to the encoder, the encoder must show audio information, I think.
I did not use possibility to save Pluto's parameters to the flash memory, I have to set every time all parameters of Pluto again. When I turn on the encoder before the Pluto, Pluto changes all box parameters - I use my own setup. It is a good idea to change encoder IP address - thank you Mike G0MJW
P.S.:We already spoken that my friend OM0MS had similar problem, it was solved after extending desktop in windows to the encoder. But it is not your problem, because your desktop is already extended.
73 de Pavel OK1PHU