Nice analysis and thank you!
At some point, there is a "line," perhaps irreversable and beyond which the off spring cannot (different from DO not)mate with parent stock. (Using the worn assumption that reproductive incapacity is the definition of a species separation).
It becomes very difficult to assign systematic differences in reproductive preference to changes in sensory coding and behavior sequences (which are likely a function of one set of alleles) versus reproductive capacity.
The adjoining postings suggest that the older, "capacity" definition of species is of limited use (although still employed sometimes for political/social reasons).
Again, we all appreciate your continued interest!