I hear it does work but I have never tested it. For some of these 3.5mm ports you have to shave the rubber on the ModMic to get it to fit. Again, I don't know if that is the case for the A40. As long as you're careful doing so won't damage the ModMic.
Because of the modular cable on the ModMic 5 I highly recommend that if you plan on plugging it into the headphone directly.
Alternatively, I have seen a couple of people do this with the ModMic where they disconnect the A40 TR microphone and feed the 3.5mm connector from the ModMic cable into the headset where the A40 TR microphone would connect. This way, you can connect the headset as intended to the MixAmp Pro TR and still use the digital mute button on the headset cable.
I would still recommend purchasing a Y-Adapter and a ModMic with a mute switch just in case this doesn't work as intended. At least you have a plan b to work with.