Hi Frank
I think you are going to run into a couple problems. First, the guitarist appears to be very into his music as opposed to being a performer. I don't know that he will do anything that will make an exciting photograph. You can try watching him to see if something he does promotes an expression other then an I'm concentrating very hard look. The trumpet player you could try shooting a longer lens, going for a face and trumpet crop, again trying to catch a peak emotional moment, straining to hit a high note etc. Also, their wardrobe shouts students as opposed to musicians (suggest dark t-shirts when the weather gets warmer).
Butch
