For the Passion cd that came out back in 1990 i believe. I have a bunch of magazines with Vai so i can check but i am pretty sure he was using the same stuff that he used when he toured with Roth and Whitesnake. He had some huge Bradshaw rigs, seems like every big time guitar player back then had Bob Bradshaw build them a giants rig. Vai did have a few Marshall back then.
And i know that during the early 90's he was using a prototype XTC.