Based on the story there's a good chance it'll be one of these recordings: https://relisten.net/grateful-dead
Assuming it’s a band most have heard of I was leaning toward Daft Punk, but maybe the Prodigy?
Daft Punk doesn't have a singer and unless it was a very early show they wouldn't have seen them smile. Most big beat shows wouldn't have a dedicated vocalist. I'd guess Underworld or Prodigy, but lean toward Underworld.
Now I"m thinking, the mention of digital formats doesn't make much sense either ^_^;