I kind of agree with the Detective.
I would love to hear Russell singing a lot of cover songs...but Symphony X playing them? I think it would be a let down, I'd rather hear their music. It would slightly shatter the SX mystique to hear cover songs at gig.
However, if Russell did a solo tour, I would freak to hear songs like Gates of Babylon or some Dio/Rainbow/Sabbath stuff. Also, some Bad Company, Kansas, maybe even Skynyrd. Maybe he can do a covers album.