Mike played us a few demonstrative versions of his songs. But nobody said anything, they just left the room. Mike humbled himself to the notion of a band kicking around an idea. It's very hard for someone as brilliant as him to put up with that.
--- I know that "humbled himself" means that he maybe thought he was wrong, but I'm not sure about the rest of this sentence. What does it mean they were kicking around his idea? Despised it?
From this I get the idea that Mike is a talented song composer and is sure that what he has composed is perfect. The band wants to change it to fit their style, and Mike has to "humble himself" to accept that.
By "kicking around his idea" they are making alterations, trying to improve on it, until they like the sound. The first draft is rarely the one that is released.