I'm somewhat in the same boat as you. I've made 3 absorbers with 2 panels of 2" OC703 each. Since these are to replace some Auralex 2", I have a lot laying around. So I put a layer in between the 703 panels in one of the absorbers. I'm doing testing now w REW. I didn't do a test that specifically targets any difference, but I'll give that a go this evening and let you know. My sense though is that it didn't make much difference.