i'd say that if you don't have a range at least as wide as russell's, you better give up the idea of singing songs from the odyssey, which is probably the hardest symphony x album to sing.
if you still want from the odyssey you can try "Journey To Ithaca" which except an high note at the end of it it's pretty much an easy song (or a part of a song...)
other SyX Songs you can sing:
The Edge Of Forever - pretty easy but still has a couple of high
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notes
first and last parts of DWOT
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- completely nothing hard about them
Communion And The Oracle
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again, couple of really high notes, but generally an easy song, the first SyX song i learned to sing.
Rediscovery Pt.II
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the first 4-5 minutes are very easy, the rest is extermely hard....
that's about it, hope i helped...
but if you want my honest opinion, leave SyX for now and focus on easier stuff like: Metallica, G'n'R, or even DT (the easier songs of course)