Thanks for the helpful replies.
Nate152: Your response confirms my understanding of the "original" ATI/AMD multi-monitor technology (described in this 2012 video "https://www.youtube.com/watch?v=Jf0X0lNFmgw", i.e., you can have no more than two "legacy" (non-displayport) connections on an AMD graphics card. Additional connections must be displayport. So, there is no way to connect seven monitors, (the six 1080P's I have presently plus the new 4K monitor I have on order), to a pair of Rx470's since each Rx470 will only accommodate two "legacy" connections (DVI/HDMI) and will require the third "legacy" connection to be made to the Rx470's displayport with an "active adapter" leaving no way to connect the displayport-enabled 4K monitor to the Rx470. Seems my best option would be something like the Strix Rx480 8GB with 1xDVI, 2xHDMI, and 2xDP. I connect one 1080P monitor to the DVI output on each card, one 1080P monitor to the HDMI output on each card, and one 1080P monitor through an "active adapter" to one of the displayport outputs on each card. When the 4K monitor arrives, I connect it to the unused displayport connector on either Rx480 8GB and I have my seven monitor setup.
Menthol: Hopefully the Rx480 8GB will provide enough horsepower to support 60 FPS on the 4k monitor.
Further comments are welcome and appreciated.