Here's the quick n' dirty answer: No.
Powered subwoofers hooked up in that configuration are merely sharing the signal with your main speakers. They do not draw any current from the amplifier, thus you are not changing the final impedance, lowering the amount of power going to your main speakers, or anything like that.
Powered subwoofers hooked up in that configuration are merely sharing the signal with your main speakers. They do not draw any current from the amplifier, thus you are not changing the final impedance, lowering the amount of power going to your main speakers, or anything like that.