IGN didn't have any contact or infos from OWI about the Steef game... at least all the things they said are simply interpretation of the X-factor, and thus probably not 100% right
Just think of higher pitched voices, and your closer.
Their voices were a suprise to me, a couple years ago when I first saw what vykkers looked like, I expected some darker deeper voices. Similar I guess to the original Glukkons.