I'm try to put B6 OEM S4 Avus 18" Wheel on B5 S4, anyone knows will fit or not fit???

It was determined that while they do fit, it's so close that when you have a full brake pad on the fronts, the caliper can come in contact with the back of the spokes. So those that have done it have used a 5mm spacer IIRC.

Explains why the BBS RC fits on the B6 though....It won't fit on a B5 with a big brake upgrade.