Excellent set of rules...personally, I would play them much more often given the opportunity!
I too like the idea of the campaign in the new Minature wargames magazine. Am not quite sure how one would represent the Goths, Franks and Huns, etc, in the Dux B rules...probably just normal non-shieldwall 'warriors' for the Goth foot, and options for loads of cavalry for Goths and Huns in their army lists... Franks would be rather like Saxons, I guess...although I'm not sure that Goth and Frankish foot should be quite so capable of ignoring rough terrain as Saxon raiders.
The Romans could either be taken straight from the Roman and Romano-Brit lists in the book, or one could create a more 'Foederate' list using Goths, Huns or Franks built around a smaller Roman 'core'.
Hun and some very late Roman cavalry should probably have bows as well as being combat cavalry...not sure how that would unbalance things, but it would reflect the noble cavalry of the late 5th Century AD.