Excellent review. We do recommend using a high pass filter/crossover at 80 Hz for the speakers whenever possible. I wouldn't say that setting a crossover will necessarily help the high frequencies but, it would definitely improve things on the mid-range driver for sure. Also, it would help free up the clean headroom of your amp because low bass frequencies require quite a lot of power to drive. So putting in a high pass filter on the mains will help give you better dynamic range/clean output. That might explain why you hear better cleanliness overall.