I think you've got it right; ANR protects in the low range, not the high end.
I bought the kit from Headsets Inc this summer and installed it in my Gentex helmet. There is a noticable reduction of noise with the unit turned on, but the biggest advantage is getting to turn down the comm and intercom volumes 25 - 50%. The comm is also *much* clearer.
The kit was missing a couple of minor parts, but I was able to cobble it together.