taxonomy menu links change with path
Sounds to me like you ACTUALLY want Menu block in tandem.


  So… have you ever used the Main and Secondary menu links feature on
  your theme and wondered “how the hell do I display any menu items
  deeper than that?”


I think the following is what you're after, but the module is pretty configurable if I'm mistaken.

Create your taxonomy menu as you normally would, and instead of putting that menu block in the sidebar (or wherever), put a menu block generated block there. Then in the settings for the menu block click Advanced. Under this tab, there's now a chekbox titles Make the starting level follow the active menu item. If you check that box, then the top level will reflect the current page.