I'm trying to find a solid speaker system that is compatible with this receiver and I am having no luck finding the answers online. If anyone could help it would be greatly appreciated
Budget? Room size? Listening habits? Musical tastes?
Without knowing what your budget is, we cannot answer you with any specifics.
Any solid speaker, made by a firm that is known for making quality speakers, such as Infinity, Polk, JBL or Klipsch, to name but four, would do fine.
Just make sure that the speakers can handle the full per channel power of the amp in the E-400