Tried the SMC reset and resetting the PRAM but the sound to my external speakers is still kaput. Tried deleting the sound preferences files as well.
This is a very ragged problem, I think. Let me explain: when I installed Lion my external speakers worked OK, except, for some reason, the left tweeter. I played around in Audio Midi Setup to see if I could get the left speaker to work, and then all speakers (tweeters, sub-woofer) went mute. The internal speakers remain operative. And one more thing: the general volume slider at the top of the screen sometimes has a little blue aura around the button (as it did in Snow Leopard) and sometimes it doesn't. And it works for my internal speakers, but obviously not for my 'dead' external speakers.
So this seems to me not like a single sound problem that can be tweaked immediately with some new code from Apple. It suggests to me something has unravelled in the sound department with Lion, but not on every computer. So finding what's causing it may take time.
Hopefully there are enough of us with this problem to actually prompt a quick response from Apple. I would hate to have no music for the next three months.