Depending on what you are using, you could actually be cutting your power. What Happens when you hook A Speakers + B speakers both up is that your Amplifier (I assume Receiver) either parallels or series the connection. So if you are using a SET of 8 ohm speakers on A, then add a set of 8 ohm speakers on B, your amp if Paralleled will see an 4 ohm load, but if it Series the connection, your amp will see a 16 ohm load. In my experience only older lower price receivers have done series wiring, but if it did, your 35 watt per channel will be less. Anything today with a decent power supply should parallel the connection. Bi-amping is done 2 ways....
1. 1 amp runs mono playing left channel, 1 amp runs mono playing right channel...
2. One amp is crossed electronically and runs tweeters and another amp is crossed to only run the woofers.
I hope this helps, Tim