Question on imput impedance and gain when bi-ampin

How important is it to match the gain and imput impedance when bi-wiring and bi-amping your main speeakers?
Depends. Do you have gain/sensitivity controls on the two amps?

No I do not have gain control on the amps.
You don't need to even know the input impedance of the poweramps unless you're filtering them passively or using a tubed preamp with high output impedance which may not be able to drive both amps well. You'll probably need gain controls on at least one pair of amp channels unless you're using identical in splitting a stereo amp 'vertically' on one speaker. Said another way, unless all amp sections have identical voltage gain (which is NOT the same as sensitivity for full power), you'll need gain controls on the amps with higher voltage gain because you'll need to turn them down in volume.