I actually am using a w810i and i can tell you for a fact that the R4ED001 FS works completely fine with the R4EA031 Main. I don't know why but they only had a few FS for R4EA031 and I have yet to find a MAIN for R4ED001. So I can only assume that R4ED001 is actually ment to be used with the R4EA031 MAIN. But like I said, you can be 100% positive that the R4ED001 FS will work with the R4EA031 MAIN