Hey all; just wanted to post here that I managed to fix it, and that fixing it brought some interesting discoveries:
-I tried doing a verification of file integrity, and Steam reported that there were 2 files that needed to be replaced (and supposedly did so). However, there was no change regarding my problem.
-I tried uninstalling again and watched the folder where it was installed - uninstalling left a large portion of the game files intact in the zero-k folder of the steamapps folder
-Deletion of all files (except my save games folder) followed by a fresh reinstall successfully restored musical function to the game.
I thought that you folks might like to know that uninstalling does not actually delete everything. I don't know if that's something that the community should fix, or whether that's a Steam problem, but I figure that someone here would be interested to know that.
Thanks for your help, Googlefrog!