The following is an alternative method...
Sound
System Preferences > Sound. There are 3 tabs in the window; Sound Effects, Output and Input. Be sure you are on the Sound Effects tab. Middle of the window select your TV where it says "Play sound effects through:".
Select the middle tab named Output.
Select your TV from the drop-down list next to HDMI, below where it says "Select a device for sound output".
Using either Finder or Launchpad go to Applications > Utilities > Audio MIDI Setup.
On the left-hand side of the window you should now see HDMI. In the middle of the window, on the Output tab, where it says "Source:" select your TV from the drop-down list.
This last action below is NOT described in the iWires notes but was required in my case, it may also be required in yours. If you CANNOT see a speaker icon next to HDMI in the list on the left, do the following:
Bottom left of the window select the wheel icon with the down-pointing triangle. Make sure that sound output is selected and that you can now see a speaker icon next to HDMI in the list of devices.
If you still cannot hear sound, log out of your account and then log back in.