Sorry this is gonna be picture heavy to illustrate (pun totally intended) the point.
One option is to write lyrics. You don't have to write an entire song, just a few lines, since I assume you're not gonna show the entire performance.
Another option is just no lyrics. I've seen even anime do this. The background music swells and the characters lips move, but you don't get the actual song.
Show the playing but not the lyrics. Look at the (many) Show By Rock mangas and you see this a lot. If you treat the music like an action scene like a lot of their Bromides you can get excitement without doing much, like so.
And then show enough of the reaction shots of the audience surrounded with typical amounts of shoujo love hearts and sparkles to get across the reaction, like the audience in the corner.