Here's my usual recommendation but the active bass aspect of your mains kinda throws this off. You may indeed want to set your mains to large and keep the subwoofer set at l/r+sub. I'm sure the G-man will chime in with some insight as well.

Set all speakers to small. For the mains and center, take the -3 db rating for the bottom end of the speaker's frequency response and round it down to the nearest multiple of 10 and then double that to get the crossover frequency. For example, if the speaker is rated down to 37Hz, I'd set the crossover at 60. For surround speakers, I usually go with the closest crossover setting that's greater than what the speaker is rated at. If the speaker is rated down to 82 Hz, I'd go with 100Hz as the crossover setting. This is just a guideline to get started, adjust to what your ears like best.

--Chuck