I have just purchased and AMD R9 390 video card, which I have installed on my Windows 10 PC.
I am using the latest CCC 15.11.1 beta drivers and got my 2x22" running at 1680x1050 monitors working nicely.
I then changed my display to eyefinity and as expected formed one desktop, so far so good.
The resolution is way to high 5120x something, so I went into the ccc control panel and changed to the resolution to 3360x1050 and nothing changed.
Doesn't matter what resolution I change it to nothing changes.
My 1st monitor is connected using HDMI and 2nd using DVI.
P.S. My previous card HD5850 was doing this fine.