I L O V E my HE-4XX too are fantastic for gaming is sound imaging is just amazing, wide yet focused soundstage; music and movies are a true delight, glad to know that you gave yourself the opportunity to try them.
Honestly, I haven't know about any issues by using the ModMic with it. However as far I research: Antilion, FAQ states it shouldn't interfiere with your headphone drivers, but HifiMan doesn't recommended and warranty doesn't apply, for me that's a no-go.
So the safest bet might be placing the holder on the frame of the driver or hooking the modmic somehow (ziptie?) at the headphone driver plug.
Never tried use the modmic on it, even though enjoy every minute I play with the HE-4XX, still I prefer the ATH-ADG1X for long game sessions, are lighter and its mic is better than ModMic5, that cable though.... I haaaate it, one of these days I going to ask to the techkies to make me the cable mod,I will do it myself, but my pulse and eyesight are not the same.