I tried individual crossovers on multiple subs a couple of years ago. It can work depending on your room acoustics and phase settings. The only question concerns the cascading crossovers. Some say you can get away with it on the EP subs because of the brick wall filters. The 40hz crossover on one sub is far enough away from the receiver crossover, that its OK. Have you tried setting the other sub to bypass instead of 80hz and is there any difference?

John