It was mentioned already, but I'd like to plug Myrath again. They are very much like Symphony X in many ways. In fact, they were a Symphony X cover band for quite a while. They also add some cultural elements to their music that make it different than Symphony X. I'd start with their album Desert Call.
On a separate note, what do people think of Lance King in general, not only as a singer, but also in terms of the music that his bands have produced. It looks like he has mainly been focusing on his record company lately, but I did like some of his work in Pyramaze, Balance of Power, and Avian. He seems a bit more power than prog (I'm no expert on this), but at least I find his music interesting.