I think you are getting some very good advice here. The R11s should in no way have that suck out from 3k to 13k, so you are either doing something wrong with the room treatments, or the speakers are defective or you have somehow inserted some kind of broad filter centered at 7k taking everything down by 15 db. (That dip is very symmetrical, so to my eyes it kind of looks like some kind of filter has somehow been inserted into the chain). I definitely find it worrying that you do have a plot with the treatments removed showing the same suck outs. I might take one or both of them outside and measure, just to see if that's somehow room related, but the KEF's should be less susceptible to room issues than most any other speaker.
Once you get that sorted out, I'd suggest you look into replacing your streamer with something like the mini-DSP Flex or SHD, both of which have Dirac Live. Dirac greatly simplifies the learning curve for a new audiophile, and provides professional level room and speaker correction which should be as good as if not better than anything that can be done with REW. Given what you already have tied up in that system, having a streamer/dac which employs Dirac seems like a worthwhile investment in system optimization. And Dirac DLBC would be best of all, as it would allow you to create a 2+2 stereo system with full correction of each bass channel. But that's only available on AV Receivers or PC versions of Dirac. If you can use a PC as your source for everything, the recommendation would be to do that and use DLBC with a four channel DAC, which would definitely be superior to Dirac Live, or most anything else.
BTW, the vertical mic position (mic pointing at the ceiling) is for home theater, not 2 channel stereo sound. For stereo, the mic should be parallel with the floor.