Ok, well mr Idiot here picked up an Netgear R7000 thinking I had this all down pat...........realized that in AP mode the R8000 & R7000 have to be connected via ethernet cable?......DOH!!!!! Please someone yell at me if that is not the case......I'm trying to setup the R7000 in repeater mode just to test 2.4Ghz signals upstairs regardless (R7000 being a pain in the ass by the way and isn't getting this right) but I'd be more curious if AP mode is handled via wireless between the 2 units or has to be hard wired. I have a message into Netgear asking this as well.
Have you thought about heat dissipation within the closet itself ? Possibly cut in a return air vent as high as you can or have an electrician install a super quiet bathroom exhaust fan?