In case there's still some doubt after Sanjay's excellent post, I'm tempted to revisit my "virtual sub" analogy. Turning on the second sub does not actually change the response of the first sub (or vice versa); rather their combined output is now heard as a new virtual sub whose response is different from either physical sub heard individually, and whose raw response can then be equalized to achieve the desired response.

Equalizing the 2 single physical subs independently before equalizing them together will certainly change the response of the virtual sub, but in a completely unpredictable and not necessarily favorable way. In addition, it wastes time and money and adds unnecessary complexity. It's simply a bad idea.