i just take the same manufacturer (i thought - i just read the bills again, they are diferent / may be just the boxes who knows ? )
the calipers are nearly the same - i didn't test if they are replaceable.
i only remember, that i readed a post that it is possible to use ther stronger springs of the a4 calipers on the 4x4 calipers ... but this i didn't tried equally.

i hope the old schoolenglish isn't so bad.