Thank you for your reply to this post. I have updated the graphics driver and several other drivers (e.g., Audio, LAN and BIOS) provided on the Sony esupport link provided in your reply. After installing INDVID-00296376-0082 and INDVID-P0317186-1082, there is a difference in the audio behavior when playing a video for display via the HDMI connector, but it is not the behavior that I had expected or hoped for.
Prio to applying driver updates, when I played a video with an HDMI cable connected to my VAIO, the graphic (video) content of the movie was displayed on both my VAIO screen and on the HDMI-connecteed remote display (A/V display system), but there was no audio output either to my VAIO speakers (or headphone jack) or to the remote HDMI-connected system.
After applying the updates, graphic content was once again provided on both my VAIO display and on the HDMI-connected A/V system, and this time audio content was provided to my VAIO speakers (and headphone jack), but not to the HDMI-connected A/V system. It appears, based on this performance test, that the HDMI output on this VAIO notebook is by design video only (sans audio content). If true, this means that HDMI output on this VAIO notebook is (by design) quite useless. The purpose of HDMI is to provide a connection that supports both video and audio content for program material, so to design or provide an HDMI capability that supports only video - without audio - content is useless and (from a marketing standpoint) deceptive. I hope I'm wrong about this, but it apears to me at this point that the HDMI support on this VAIO notebook is useless for my purposes (and for the purposes of the majority of users in the world).
If you think that audio content should be being provided via the HDMI output connector on this VAIO notebook, please let me know.