The input sensitive is the amount of current required for the amp to reach full output. For example one amp might require one volt , another two volts. This is the governing factor in the choice of amps in this case I would think. Input sensitivity is always specified for a power amp , I am less familiar with voltage gain. I would assume that it is the mirror image of sensitivity, describing how much the initial preamp signal is amplified. But it is not necessarily the case that you should have equal output from both amps. The tweeter or tweeter/midrange will require much less power than the woofer so having the same output from both amps might overdrive the high end. In the past when amplifiers were offered with several amps on the same chassis the treble amps were always of considerably lower wattage than the bass amp .I think we are saying the same thing with different terminology. The critical factor is the bass amp having greater sensitivity
( higher voltage gain) so that it can be adjusted by a volume control as we have both suggested.
( higher voltage gain) so that it can be adjusted by a volume control as we have both suggested.