Boulder indie-folk hero Gregory Alan Isakov is again teaming up with the Colorado Symphony in August. Rebecca Caridad Singer-songwriter Gregory Alan Isakov has been mesmerizing audiences with his singular indie-folk sound since moving to Boulder in 2000 to attend horticulture school at Naropa University. But there is something to be said for collective sound. As in, playing with an entire symphony behind you. “There’s something so magical that happens when we play with a symphony,” Isakov said in advance of his two upcoming appearances with the Colorado Symphony at the Boettcher Concert Hall on Aug. 19-20, which are expected to be sold out by this weekend. “It’s a holy experience.”…