Jim - You are correct, the EQ circuit boosts the bass starting at 300Hz to 12dB at 25Hz. Our initial intent was to EQ the woofer and leave the midrange and tweeter unaffected, but the slow XO slopes required grouping the woofer and midrange to keep the frequency response correct - resulting in far less efficacy for the bi-amp idea.
Note that any perceived differences in the upper range caused by the EQ are indeed real. They are artifacts. In that regard the CS3.5 EQ was a performance advance, and is a drop-in swap.
Note that the bi-amp configuration caused more problems than it solved. For one thing the tweeter-only amp is a lot of cost for little return. Also, to maintain proper frequency response, the two amps must provide equal gain into these particular loads, which is far from trivial. Likewise, the cables must be the same as well as same lengths to maintain proper time alignment.
Our rather extensive testing confirmed that a single amp and single cable always outperformed the bi configuration. Going forward, we swam upstream with that single input approach.