Say, for instance, the action speed boosts on Frenzy (or Swift Strikes) and the modifier on the Chromoprismatic staff ?  Or are they both considered active buffs, with only the highest taking precedence?

It seems MaxQuest indirectly answered this in his last post in the Attack Speed mechanics thread.  Short answer: yes, the item effect stacks in this case.  I think.

They stack. Even buffs activated from items will typically stack with buffs granted from abilities, though modals granted by items won’t stack with active abilities.