Do you have an on board sound card and sound cards like Sound Blaster. If so.
You must go into the BIOS and disable the on board sound device.
Does the sound work on other flash web sites?

Sound is on-board, no sound card

Kmix shows all settings at max

Hint: I think this is a permissions issue/conflict someplace perhaps
because of the way I do things here. I am logged into the system as
user1, then I "sudo login" to several other users, each having their own
workspace. Sound works from root and user1 but not from any of the
other users. User/Group administration has all users set to "use audio
devices". System is confused. Or, more likely, I am.

I would look at KMix and check that all of your channels are available,
particularly PCM. For some reason, the *buntus like to ship with some things
muted or sliders slid way down.

Try this: https://wiki.kubuntu.org/DebuggingSoundProblems