It basically came down to Berman wanted the show's theme to be Faith of the Heart, Braga wanted U2's Beautiful Day. The rights to Beautiful Day were way too much for the show to afford
I'm confused now. It's been about six months since I saw the ENT Season 1 VAM, but the impression I got was both Braga and Berman were into U2, but U2 didn't want their song on a Star Trek show full stop. That's when they went to Warren.
I could be absolutely wrong about that though.