Here's what I'd suggest:
- Fronts (rated 38Hz-20kHz): Small, 60Hz crossover
- Center (rated 68Hz-20kHz): Small, 100Hz crossover (might also try 80Hz)
- Surrounds (rated 46Hz-20kHz): Small, 80Hz crossover
- Sub: On (no choice there, with all speakers small), and set the crossover control on the sub as high as it will go. I didn't see a bypass option on the sub's controls, so buy setting it as high as possible you avoid having the 990's crossovers and the sub's crossover overlap.
Hope that helps.