Irascible: It looks like all the Titus diffusers are either adjustable or could be partially blocked to restrict airflow and increase velocity. Two of the largest ducts are the ones that go to the LR (21" round) and BR wing (18" round) both are under a poured concrete slab.
Dan: Does "direct radiation path" just refer to being an outside wall or to heat gain from direct sun? The former is true but there is an original 9' overhang on that side so there was really never any direct sun before the solarium was added.
Any other thoughts from anyone regarding ducts that are much too big?