How about installing the hynix card first? can you do overclocking?
there is this settings in the MSI AB to untick the Synchronized settings for similar graphics card in order to set clocks individually.
I am just wondering on the greyed out issue, that problem is seen in incompatible driver to MSI AB versions, however you've told that its working on 3 gpus so its kinda weird.
The 4 GPU's worked when I used them all individually, just not when I have them all connected. I only have 1 Elpida card and 3 Hynix cards. Not even sure why since I ordered them all from the same link on Newegg.
I will try unplugging the Elpida card and see if Afterburner works on just the 3 Hynix cards.
I think that is it without a doubt. If you are running that many cards you simply need to bios mod them 1 at a time