Please do not post any links until you have 3 posts as they will automatically be rejected to prevent SPAM. Many words are also blocked due to being used in SPAM Messages.
Thanks!
Check your audio properties in Windows to see what is set as your default audio device. Its probably set to your onboard and you'll need to change it to over to the HDMI.
I don't think there is a way with onboard sound and windows drivers. You typically need a separate sound card (from onboard) that'll let you mirror the sound across 2 devices.