It is extraordinarily difficult to tell whether plants are orientalis or domingensis, eben in the hand. Almost impossible in a photo. https://vicflora.rbg.vic.gov.au/flora/key/2087
Identified as T. domingensis 3 years ago http://canberra.naturemapr.org/Community/Sightings/Details/32789 but I see what you mean about distinguishing the two. Even measurements of leaves and flower heads will have overlap.
I think the thinness of teh spike that they are cinnamon brown and have a break in separation makes Typha domingensis more likely, but a Betty points out this is not certain