I have the wires plugged into the 260 for feeding my HDMI TV on occasion.
I am using an MSI p55 GD85 MoBo with the Realtek sound drivers
I found that I had to go into the Realtek control panel and switch the defaults sound output from one to the other depending on which one I want to use. It seems to not be able to send to both. The sound defaults to one or the other not both as far as I can figure out. You may have the sound going to the HDMI and need to change the default to the rear panel speaker jack