Attack!! is an album that included the keyboardist from which group from 1994-99?
Attack!!:  The album is the first to feature singer Doogie White on lead vocals, along with keyboardist Derek Sherinian. Derek Sherinian:  He was also a member of Dream Theater from 1994–99, is the founder of Planet X and also one of the founding members of Black Country Communion and Sons of Apollo.
Dream Theater