I've tried bi-amping my 70's off of my receiver and to tell you the truth, it really didn't do anything that I could hear.
You may want to just consider not bi-amping and just do a 5.1 set up, you'll actually be sending out more power to your speakers, check out a bench test on your model receiver and it should tell you the power output with 2ch, 5ch and 7ch driven, it's always the most power in 2ch and the least amount of power in 7ch.
And when you're bi-amping, you are essentially in 7ch mode.
Even though I'm using a separate power amp for my 9's, I removed the jumpers and did this;
My speaker cable is 10awg and I'm connecting the upper terminals with 12.