We haven't started updating the Impress Guide from OOo to LO, and as I recall sound was often an issue with OOo: it worked, but not necessarily the way the user wanted. But you're saying it doesn't work at all with LO? At least not on Windows? Any particular version of windows? And is this LO 3.3?
My first thought: is this one of those things that needs "experimental features" turned on?
The LO Impress Guide is next on my to do list, so I'm interested in pursuing this. In fact, I should check the OOo info more closely too, in case there is some problem there too. I've had no experience using sound in presentations, but it's something I want to learn more about; and now that I'm home for awhile, I do have some Windows machines to test on.
With luck, someone will know a lot more about this and reply here, and save us all a lot of work.
--Jean