Thank you Justin Durand for pointing out this fantastic new Internet site:
The Making of Charlemagne's Europe: Legal documents surviving from the reign of Charlemagne: (http://www.charlemagneseurope.ac.uk/charter-collection-short-refere...)
Between this and Cawley's Medieval Lands (http://fmg.ac/Projects/MedLands/CAROLINGIANS.htm#_Toc240955192), all our armchair historians on Geni should be able to get Charlemagne's tree to a very respectable level of academic sourcing using primary documents!