"I am wondering if I could plug my 100s into that receiver and then hook another speaker wire going from the A5 and hook that into the other plug on the 100s."
You could, but unless they have the exact same power, you would have different volume levels from the Highs verses the lows. It would not be advisable. Biampable speakers have a separate input (speaker posts) for a) their highs (mids and tweets) and b) the woffer. You are bypassing the crossover in a sense. If you use different amplification sources you will not be able to give the exact same power to both inputs at the same time, and therefore will not have the speakers perform the way they were intended.
"Also, when I hook up the speakers, is there a difference between the top and bottom plugs on the speaker?"
If you do NOT biamp you can use either set. There is no difference. Make soure the jumpers are in place. If you ARE biamping make sure the jumpers are REMOVED or you will notice an unwelcome oder coming from your amp.
I have a PVA7 that runs a 5.1 system. My extra two channels of amplication are being used to biamp my fronts. I split the signal coming out of my pre/pro (you could use the pre outs of a reciever) for my front left and front right and sent the "extra" signal to the rear surround amp channels. After i removed the jumpers i biamped the fronts.
Be very careful when you biamp. When done right it sounds great.