Lapazeus
I think that the fun part is when you have to quess/(or should I say) know which sections are neo-classical and which are actually already composed by someone else. And BTW who listens to neo-classical music and not the real thing said:
You would probably be surprised to find that there are plenty of people. There are the fans who know all of those excerpts and where they came from, fans who know some of them, fans who find those excerpts familiar but don't know the pieces well enough, and fans who are not familiar with the "real thing" at all. And there's nothing wrong with being in any of those categories. I know several people who are really into metal and got into symphony x that way, and have no idea where some of this stuff comes from. Some are interested in hearing more, some aren't. I think it would be a wonderful idea to cite them all, either in the liner notes or on the website, with something in the liner notes directing you to the website for more information.
That having been said, I don't think Symphony X is being dishonest in any way. The music is considered "public domain" and isn't required to be cited. They aren't trying to trick or deceive anyone into thinking they wrote anything either. The name of the band alone gives you some indication of what they are about. I don't think it's anything to be concerned about.
Chris