You can get the ACH / MICH adaptor direct from Eye Tactical for quoted to me at $15. The only difference is the top part that goes above the screen and connects the straps, it is a seperate peice(as well as many others) that comes off and you just need to put on the ACH version and it will fit correctly with those helmets. The ACH version has straps that go up and over the helmet from the front corners and leaves the front open to vent outside of the helmet, and allows for nightvision mounts aswell.

I was going to get it but put of gettin the ACH helmet and did not need it yet.
See the instructions here from Eye Tactical themselves for a better explination of what I am talking about.