Can't please everybody, but we have to work with what we're given.
And who knows, you may end up liking Yuya's music, too? That's the whole point of MusicFest...to bring established fan-favorites like FLOW, but to also introduce new artists/bands coming into the scene who may have some really decent connections to anime and/or may appeal to the general audience that comes to FanimeCon.
But the general way to get into MusicFest is pretty simple: you line up, you grab a seat, and just let yourself enjoy the show.
If you were to see FLOW in Japan, you'd probably have to sit through several bands before reaching FLOW's set since they tend to do shows with up to 3-4 other bands. Recently, a lot of their one-man lives are limited and/or only for fanclub members.