Two recipe questions:

Can I use a yellow cake mix for it...and would I use 3 eggs instead of 4 egg whites?

Also, if the previous yellow recipe works could I add peanut butter to make a PB cake?

Thanks!

I make the WASC with yellow/white/chocolate all the time and I always use three eggs (obviously I've never tried for a really WHITE white cake). Anyway, it works fine. If you're going to add peanut butter, you might want to cut back on the sour cream a little, so the cake won't be too heavy or greasy.

http://cakecentral.com/recipe/the-original-wasc-cake-recipe

This will answer your ?s
YES! you certainly use a yellow mix and 3 whole eggs.
I don't remember ever adding PB but I bet it would be good although probably mild in flavor.