I initially set out to copy the basic Winger sound, just so happened that intro to Hangin' On was easy to zoom in on and copy the exact delay between the tracks which I believe was an Eventide effect. The hard part was what IRs could copy that analog flitering sound. I just so happened to have made an IR of the Eleven Rack's analog delay "color" that reminded me a lot of it, so used that, then tried to EQ it to match the frequencies. Took me about 20 IRs until I was finally happy.
I will post the last two I liked, because the first one does work well over the Winger backtracks. The one I used to record with just had a better feel for me overall.
I just used the Dokken preset I have been playing through a lot latey, so results will vary with other presets and guitars probably too...
IR (used in recording): http://1drv.ms/1ljpZkX
Previous version (Closer to Reb Beech sound): http://1drv.ms/1ljpZBy
This wasn't from the ground up, with the right cabinets or anything like that, so it probably more like what Vai would have going with a bunch of different cabinets belnded on one side and the Eventide doubling effect on the other.