I did some vent and damper mods, but chose to do them a bit different from what Rin suggested, as I'm not strictly going for measurable flatness. The major change was that instead of replacing the cloth damper with a Knowles damper for the ED driver, I didn't use a damper at all, and chose to not use any resistance adapters.
The result is something that is not flat, but rather somewhat peaky, resolves harshness more than most would desire, and has a bit of bass boost, but I feel that there are some benefits to the mod. First, not using a resistance adapter keeps the damping factor on the dynamic woofer high, retaining the most texture. There is still more bass than measurable flat, but the vent mods help tame the mid-bass and the quantity isn't unreasonable. The lack of a damper for the highs, helps give a "raw" presence to the midrange. The resultant response really isn't all that harsh in the grand scheme of things. At least, it's not harsh compared to some things that I've heard before. People can still adjust high frequency response to get to their desired quantity of treble with a resistance adapter, but the harshness that stems from not using a damper will show up much earlier. That's why I don't normally use a resistance adapter with the mod anymore.
Right now, I'm working on cutting a center hole inside the cloth damper to allow the BA not to be filtered, but to still filter the dynamic driver. The goal is to emulate the filter on the AX60.