Ever since the days of Jethro Tull playing a flute and including Tolkien runes on their album covers, symphonic rock and D&D have had a place for each other. Bands make songs that include fantasy elements, and we play them during D&D sessions.
The queen of D&D symphonic rock has to be Nightwish. The Finnish band has a fantastic sound that combines classical and rock easily. My favorite two albums are Nightwish (below) and Century Child, both featuring Tarja, the former singer of the group who was dismissed publicly a few years ago.
If you haven't heard of Nightwish, it's time my friend. I changed my entire soundtrack for my last campaign with Nightwish as the inspiration