Note that since SAXS restraints are expensive to calculate, you may
have better luck using SAXS as a filter on your final models, or
perhaps generating ab initio SAXS shapes as input to the optimization.
I would strongly advise against using saxs shapes to do fitting. The 3D
shapes are highly degenerate. Use the PMI saxs restraint and find the
correct weight (adjusting it over the course of the simulation if
necessary), or resort to filtering if you cannot do otherwise.