Butch, as was said previously, there's no possibility of actually biamping with a receiver which has only one amplifier feeding through several channels. To even start on biamping two separate amplifiers would be needed, as the term implies. Also, an external crossover(with the internal speaker crossover removed or bypassed)before the amplifiers would be needed so that each amplifier would be sent only the desired frequencies.
On your question about a 4ohm speaker turning into an 8ohm speaker, no, each section is nominally 4ohms by itself. 4 ohms doesn't come about as a result of two 8ohm sections being driven in parallel. The action of the crossover keeps the impedance(roughly)at 4ohms.
