Is 80Hz always the right crossover setting?

It is the right starting point, not the right answer. 80Hz keeps the sub unlocatable and unloads small woofers — the convention THX popularized. Move it up (100–120Hz) for small satellites that strain below 100Hz; move it down (60Hz) only for towers with genuine low-frequency capability. Then verify by ear with a bass sweep: you should not be able to point at the sub with your eyes closed.