Jostler, you are right and I stand corrected. Here is the real scientific explanation on why biamping effects sound. This came off the net if anybody is interested. When a current is pushed forward by the amplifier through the voice-coil in the magnetic field of a loudspeaker driver, the voice coil and attached cone move forward - the electric motor effect. However, the voice coil moving in the
magnetic field generates a back voltage - the electric generator effect. In a perfect driver, the back voltage matches the forward voltage, giving rise to the driver's dynamic impedance. In the real world, the back emf is distorted by nonlinearities in the magnetic field etc giving rise to harmonic distortions and so does not exactly cancel the forward voltage. These harmonic products from one driver's terminals end up across other drivers in the loudspeaker if they have common terminals and can cause further muddling of the sound. By connecting each driver through separate leads back to the amplifier, the distorted harmonics generated by each driver can be short-circuited by the low impedance output of the amplifier. The ability of the amplifier to sink this back emf from the low frequency driver is the damping factor. Where I went off course is not knowing that when the jumpers are removed the crossover is in effect halfed, so that the amp always sees the same impedance and does not effect damping factor. There now I feel better.