Most likely somewhere in between. But it's not possible to define a specific answer because there are too many variables involved, including the frequency content of the music, which is constantly changing.

If the amps are rated at 200W into 8 ohms, and if the impedance of the speakers is close to 8 ohms at all frequencies (which is unlikely), 200W will be available at frequencies that are substantially below the crossover point, and another 200W will be available at frequencies that are substantially above the crossover point. But since music consists of many frequencies that are present at the same time, the answer will vary depending on the relation between the specific frequency content of the music at any instant of time and the frequency of the crossover point, as well as the slopes of the crossover.

Depending on the voltage swing capability of the amplifiers, the answer may also be affected by whether the biamping is done passively (using the crossover network in the speakers) or actively (using an electronic crossover between the preamp and power amps).

It's even possible that under some circumstances, at some instants of time, more than 400W may be available. To cite an extreme example, if the amps are solid state and are rated at 200W into 8 ohms, and the impedance of the nominally 8 ohm speakers is more like 4 ohms at low frequencies and 12 ohms at high frequencies, the low frequency amplifier may be able to deliver 400W by itself at those low frequencies, and the high frequency amplifier may be able to add to that another 133 watts or thereabouts at high frequencies.

Regards,

-- Al

If the amps are rated at 200W into 8 ohms, and if the impedance of the speakers is close to 8 ohms at all frequencies (which is unlikely), 200W will be available at frequencies that are substantially below the crossover point, and another 200W will be available at frequencies that are substantially above the crossover point. But since music consists of many frequencies that are present at the same time, the answer will vary depending on the relation between the specific frequency content of the music at any instant of time and the frequency of the crossover point, as well as the slopes of the crossover.

Depending on the voltage swing capability of the amplifiers, the answer may also be affected by whether the biamping is done passively (using the crossover network in the speakers) or actively (using an electronic crossover between the preamp and power amps).

It's even possible that under some circumstances, at some instants of time, more than 400W may be available. To cite an extreme example, if the amps are solid state and are rated at 200W into 8 ohms, and the impedance of the nominally 8 ohm speakers is more like 4 ohms at low frequencies and 12 ohms at high frequencies, the low frequency amplifier may be able to deliver 400W by itself at those low frequencies, and the high frequency amplifier may be able to add to that another 133 watts or thereabouts at high frequencies.

Regards,

-- Al