Some people seem to want to put materia on U/U gear but i think it should stay crafter only, what i suggest is if you Spirit bond max an U/U item it makes the existing stats on the item better.
For example the Sipahi Turban would become +10 STR -6 enmity and +6 wind resist. These are the stats before the item becomes stronger Str +5 enmity -3 and wind resist +3.