I don't know if there are any 970's paired up with Orbs yet or not. The specs were a little elusive at first, but I found them. The overall system inluding subwoofer is rated at operating from 28Hz to 20,000Hz at +/-5dB (which is a wider allowance than the standard +/- 3dB)), but the satellites themselves have a frequency response of 80Hz to 20,000Hz (presumably at the same +/-5dB). Based on that, I'd recommend a crossover of no lower than 100Hz, and I might toy around with 120Hz as well.

The new Model 7075 would potentially be a very good match for these speakers, but you could also go with the Model 7125 and be in a position to drive larger speakers a few years down the road without investing in a new amp.

EDIT: Here are some more detailed specs that would lead me toward the 120Hz crossover point (the review's specs page indicates frequency responses of 80Hz to 20,000Hz at +/-6dB and 120Hz to 18,000Hz at +/-3dB).