Do you think that DT's "Awake" sounds like the same album as "Scenes From A Memory"? SyX's style really is very predictable, particularly the guitar/keyboard duels idea, and they haven't significantly changed their general sound since "The Divine Wings of Tragedy". Michael Pinnella doesn't really have a wide palette of keyboard instruments either.
There are power metal influences all over the place in Symphony X. The most obvious is Russell Allen's falsetto power metal voice. Michael Romeo plays plenty of galloping riffs, and other static riffs. His neo-classical shred solos are very power metal. Jason Rullo uses the double-bass drums A LOT. I think the most progressive thing about them is the bass playing, because it is not always totally dependent on the guitar. I think SyX are prog-influenced, but still a great power metal band.