How are you bi-amping? If you're connecting two sets of wires to two different outputs on the same receiver or same amp, then it's completely useless.
...to two different outputs on the same receiver or same amp
with a single, common power supply... (Which is how nearly every receiver is designed.)
To expand upon what he's saying. The amp in the receiver is rated for x Watts into n channels. That isn't so much because of the design of the output stage of the amps as it is the power available in the power supply.
Running the full frequency output of one channel to both the high and low range of a speaker will provide the same amount (actually for most content, more) of power to the speaker as pushing two channels with full frequency content into a split, passive cross-over network of the same speaker (and thus turning the unplayed part of the content to heat).
The only way a single amp/power supply can gain anything by bi-amping is to remove the cross-overs from the speaker and perform active crossing-over before the signal is amplified.
Don't believe us? Get an SPL meter, play a passage a good volume level, where you think you'd be getting a benefit from having two amps. Record the peak value. Now remove the bi-amping, don't touch the position on the volume control, and play the same passage again. If the bi-amping was doubling your power you should lose 10 dB. You won't. You shouldn't lose anything it may actually end up a little louder--if you were being current limited by running the same content through twice as many amps.
