Anyway, my previous post is bogus. I have since realized that when I issue the pulseaudio --kill command, it does kill the daemon, but it then starts right back up under a new pid. So I really was restarting it without realizing it. I guess my next attempt will be to see if there is some sort of udev event when I plug in the HDMI cable. If so, it might be possible to create a rule which restarts pulseaudio. Seems kludgy, but it ought to work.