http://www.mazdamotorsports.com/pdfs...x7_8691_cg.pdf

Toggle down to page 473 of the link provided above and look at the left hand side of the document entitled "rear suspension." There is no differentiation between an S4 hub whether it is a 4 lug or 5 lug setup but there is a difference between an "axle flange" for standard duty(std) and heavy duty(hvy). Thus when doing the conversion on an S4 all you need is the heavy duty axle flange and the heavy duty rotor from another S4, although I am not sure if you need a different brake caliper to complete the conversion. In other words, if the parts are coming from a 5 lug S4 you "don't" need the hub from another car for the one that is there already will suffice.