First of all you're trying to basically turn a passive crossover into an active one. Second of all you're doing it wrong. Third, it's been discussed before, but using a receiver as an amp isn't advisable for quite a few reasons.
Most importantly, as Grador said, what you're trying to do is impossible. Get rid of the SR4001 from the audio chain and either use the Behringer for sub EQ (although I guess you could bypass audyssey and use it to EQ your mains) or get rid of it altogether and just use Audyssey.
If you really want to actively cross the towers you have you'll have to open them up, take out the passive crossover, add a third set of binding posts, rewire everything, measure each driver to figure out what the optimal crossover point would be, model everything, factor in the cabinet to your modeling, buy an active crossover (miniDSP, behringer, etc) and then invest in some external amplifiers. Unless you plan on doing all of this, stop what you're doing and just enjoy the towers and 709 and focus on bass management with the 2496.