After looking at the manual I would use the rca line level (preamp) outputs from the Krell in to the sub and the XLR (balanced) output from the krell in to the amp for your main speakers. This will send full signal to both sub and speakers. Not at all sure why you're concerned about sending full signal to your speakers.
Once you are hooked up you will need to listen to the system to get the sub gain and crossover adjusted. Agai, not sure why you want to bypass the sub's crossover, it's there for a purpose. It may take some time but it's possible to get good, balanced sound this way. Good luck.