If the multi-channel system is utilizing the balanced cabels, why not just use unbalanced for the 2200/minis ? That way everything else stays the same.
I'm assuming your using the jumper on the minis to drive the woofers, otherwise, you'll need to split the signal with a y adapter at the 990 runing one of the cabels to the 2200s (and then speaker cabel from the 2200s to the high frequency section of the minis ) and the second directly to the low frequency section of the minis. Since the mini low frequency section doesn't hav a balanced input, i think this would probably be the preferred set-up.