Hey, made an account as I have the same problem, no sound at all when I try to play Moonquest, though I haven't tried the other packs.
I downloaded the file posted above but when I went into my assets folder there were not any sound files of any sort, just a couple called avatars and packs. I dropped the file in there anyways and it didn't work.
I read what Lathan posted above, did some digging around and found that in the cache folder, there is another called "org" which has a file called "lwjgl", sure enough the files within were at 2.9.0 as he said they were. I downloaded a file for a 2.9.1 lwjgl(found here: http://lwjgl.org/download.php ) and tried replacing them but when I loaded the game the files were reverted back to the original 2.9.0.
I don't know if this will be found helpful by anyone but I thought it was worth posting, I'm tired of Creepers silently creeping up from behind :/