Just apply the update again.

NOTE: I know suggestions frequently say download again and use a different USB stick. I've had it work for me multiple times with the same USB stick, and the same download, but having to apply it more than once. It seems like the update procedure can be "iffy" - but multiple tries to the same version eventually get everything sorted out. Having said that, if it continues to not work I would then take the larger effort to download again and use another USB drive.

UPDATE: I re-read you're post and since you did already apply the update again with the same result - definitely try a new USB Drive and download.
If it still doesn't work, I would go back to your previous version - and if that doesn't work I would call be concerned that the spark could have damaged something regarding the audio circuitry (and call Stern tech support).

Have you gone into the Test Menu and tried to test audio to see if you get ANY sounds??? Definitely do that, and post the results.