I have heard a biwired setup and it was no different than any other day of listening.
Semi's explanation of the theory is correct.
A sound signal from a single source cannot magically be split simply by making the cable ends at the speakers split into 4. All speaker posts would still receive the same signal and the speaker's internal crossovers would determine what range of sound is played by each driver. Of course by the time a crossover begins to work, the cable is no longer in the chain of events and has no influence on sound.
Biamping is a different story. You are essentially powering the drivers with different units hence each driver is actually receiving its own unique signal. Even still, if the amp blocks used were the same, i highly doubt you would notice such a vast difference that it would matter.
