Allow me to get touchy feely. To be an audiophile all you need is a desire to get the most out of recorded music. I started out with a table radio listening to FM. As I write this I am at my home office desk listening to my mini system(purchased from Best Buy under $1k).
Secondly, you are not talking about bi amping. If you are running two pairs of speakers off one set of speaker connections, you either run them in parrallel or in series. Parrallel means you connect both set of speaker wires at the same reciever speaker taps. Series means you connect one speaker to your receiver then connect the other to the first speaker. If the resulting load is to low you can cause your amp to oscillate and even blow. If the resutlant impedance is to high, you frequency reponse curve will look like a roller coaster(Raul, thus is true with tube and ss)Courtesy of another Audiogoner, here is how you calculate it:12-01-04: Elgordo
For speakers in parrallel it's R1 X R2 divided by R1 + R2, where R is the speaker impedence. So two 8 ohm speakers would be 8X8=64 divided by 8+8=16 for an answer of 4 ohms. In series it's additive so two 8 ohm speakers would be 16 ohms.
Elgordo
From your description you speakers were hooked up in paralell. Doing the math in my head that yeilds 2.4 ohms. This could indeed cause some amps to oscillate. In sereies the answer would be 10 ohms. Too high, but probably will not damage your amp. Onkyo made some of the best receivers and maybe able to handle a low load. Check your manual.
I violated a rule: The right answer is usually the simplest one.