I'm very attracted to the Aubisque but as in every other time I consider an Audax bike I know I will need luggage carrying capacity so I always default to a tourer. But with the Aubisque, I wouldn't get the luggage (full camping) and it would be as heavy as a touring bike anyway.....
I'm going from memory here, and I would need to check drawings in more detail than I have time for right now, but to the best of my recollection...
Rear triangle is the same in Tourer and Aubisque, except that Aubisque probably has 5mm rack screws not 6mm like Tourer, and Aubisque chainstays aren't flattened for tyre clearance.
Main triangle is the same material, 725. The bigger bikes have bigger top and down tubes than the small ones, and these changes may occur in different sizes in the 2 bikes, I would need to check. However, Aubisque being a newer design has ovalised tubes for maximum (lateral) stiffness from that weight of tubing.
Low rider bosses...both bikes
smaller Aubisque has the same offset and head angle as Tourer.
Aubisque chainstays are probably a bit shorter, at least in some sizes.
My conclusion is that all bikes are more similar than different; there is more weight differences in the cycle parts than the frames; all the Spa steel bikes are 725 main tubes and Cromo forks and stays, and this is mainly because I think the advantages in having the factory work with what they are used to outweighs any advantage from having a more exotic material. (for example, in the newer designs, the chainstay is bent to "thread the needle" between the chainwheel and tyre, flattening the stays is not necessary.)