As Satie says, you can use a passive line level crossover rather than an active crossover. Actually a PLLXO will outperform an active XO. I can provide you with the values if you decide to go this route. BTW AndyR has some analog active crossovers that he is no longer using - you might want to contact him to see if he wants to unload them. The cheapest approach to a quality active xo would probably be a DIY using modules from Ron Elliott. The DIY does not require great skills -- just a bit of soldering. Cost would be around $100. Again, I will be happy to assist you in getting the right components and modifying the boards to work for first order filters.
You do not need to use identical amplifiers but the gains (not sensitivity) should be the same. If the gains are different this can be compensated in the crossover.
Note: A passive crossover is amp and preamp dependent and changes in these components means changing the resistors and caps in the passive. They work best with SS preamps (low impedance) and amps with impedances above 50 Kohm.
IMO biwiring is a waste of wire.
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