Here is a link to the Memorial Stadium location where the band competition is held. Take the Broadway exit off of northbound I-5 in Everett.

You can park in the nearby neighborhoods off of 37th, or you can make a U-turn on Broadway and enter the long driveway to the stadium parking lot (near 39th on the map). Its kind of hard to explain - best to look at the satellite image view, zoomed in on the stadium.