jchussey - the CS3 EQ is approximately the same as the CS3.5. You could substitute them. The CS3 EQ starts a little higher at about 100Hz rather than 80Hz for the 3.5 and maxes out a little higher at about 26Hz rather than 20Hz for the 3.5.
Look at the CS3 Stereophile review to see the curve. The response without the EQ will be the mirror image of that boost curve drawn below the 0 axis.
The CS3 and 3.5 are identical in intent. The tweeters are the same, the woofers are the same except the 3.5 cone is coated for a smoother response. Rob has that coating that you could apply. The midrange is the big difference. The original SEAS wasn't up to the task and overloaded in the lower mid / upper bass and sometimes failed. The ScanSpeak 3.5 mid was far more robust and broader range. Note the sculpted baffle edges of your CS3s are true conical sections, which are a bit 'better' than the single radius curves of the 3.5.
I am treating the 2 models the same, they will get the same new tweeter and midrange built on the CS3.6. And the EQ will be substantially better. It is prototyped and sounding good.
