As far as I know all automotive differential applications that are not part of a transaxle are of the hypoid design. I have never heard of an ancillary gear set so I tried to search for Ancillary gears on the internet and I could not find any definition that would help me. The front differential on all 4X4 trucks flip the diff upside down for ground clearance and to minimize front driveshaft angles. In order for this to work they use a reverse direction cut and the concave side of the tooth is actually the drive side and the convex side is the coast side. Opposite of non-reverse cut diffs that are used in the rear of the vehicle.
I personally believe synthetic is better. Just because it doesn't stick as well that doesn't mean that it can't protect the gears. In fact this feature causes less drag and removes heat better without sacrificing metal to metal protection qualities.
