Dual Monitors with AMD video cards

Software & Operating Systems Linux
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So I posted this over at the linux4noobs subreddit at first, but it doesn't seem anyone there had a answer for me. So I figure I'd try here next.

I need a bit of help here. I have a system with two AMD graphics chips in it. My primary one being my HD Radeon 6850 card and my secondary one being my APU's built-in GPU. (A10-6800K.)

I want to use my primary monitor on my HD Radeon 6850 and my secondary monitor hooked up to my A10-6800K's GPU. My thought process is to let my A10-6800K's GPU take care of the workload for my secondary monitor so I can help save resources on my primary card/monitor.

This all works fine right out of the box with the open source drivers. But as soon as I switch over to the proprietary drivers, my primary monitor/card stops working, resulting only in video output from my secondary screen.

My first thought in trying to correct this is going to the AMD Catalyst Control Center (in sudo mode) and seeing what I can do there. I noticed that the CCC reports both of my cards there, so at very least my system still recognizes my primary card. However, the options for it are very limited. By default, it has the card disabled. And when I do enable it, it does not allow me to change any of its properties. It only has one resolution listed for as well. (680x420) So I can't even change this. And just for the heck of it, I gone ahead and enabled the monitor this way just to see if I could get the card to work at all. But after the required reboot, CCC switches the card back to disabled, putting me back at the start.

I checked Xrandr. However, it only displays information about my secondary GPU. I used lspci | grep VGA and found even there that it shows my primary GPU. So it seems to me that while the system sees my card, it's not actively being used by the X server, thus why Xrandr didn't display it.The only thing I could come up with is that the X.server isn't loading it up. And when I went and put sudo Xorg -configure in the terminal, it wouldn't let me run the command because the server is still running on my secondary GPU. I closed out the X server with sudo service gdm stop. After that, I ran sudo Xorg -configure. And it created a new xorg.conf file to run off of. I then did a mv xorg.conf.new xorg.conf command to rename it and then moved it to the proper folder with mv xorg.conf /etc/X11/. I assumed it would allow X server to run on my primary GPU. However, it didn't work for whatever reason. So I'm still at a loss.

And I'm not sure what I can do to make this work under the proprietary drivers. I get the feeling that it is probably something simple I am overlooking, that's why I need help. Any and all help is greatly appreciated.

As some side notes, I made sure that dual graphics is disabled and that the computer treats my primary PCI Express card as my main display in the UEFI options. I'm doing all of this under Ubuntu GNOME 14.10.

2

My recommendation #1: Don't use dual graphics. There's issues with NVidia dual-graphics as well.

My recommendation #2: For the display, use either just the GPU's outputs, or use the on-board outputs

My thought process is to let my A10-6800K's GPU take care of the workload for my secondary monitor so I can help save resources on my primary card/monitor.

There's your problem, Dual-Graphics doesn't work like that. I had an A10-5800K and a Radeon 6770 and it was a pain getting the BIOS and Catalyst settings right and I made a similar mistake.

TL;DR Dual Graphics lets both GPUs work on a given task, not use multiple GPUs and their outputs.

EDITED FOR CLARIFICATION

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At the bottom of my original post I said I disabled dual graphics.

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Lets say you have monitor (A) plugged into your onboard graphics and monitor (B) plugged into your dedicated GPU. Only one GPU's outputs will work, meaning that only one of the monitors will be detected, meaning that you'll only get one monitor with an image.

http://support.amd.com/en-us/search/faq/20
  Any AMD Eyefinity technology configuration that works with a single graphics card will work with AMD CrossFire™ technology, however all monitors must connect to the primary graphics card.

I don't know if this exactly applies to you, since I've never used eyefinity, but dual-graphics is crossfire, unless you're using a laptop, in which case it's some sort of graphics switching that enables the larger GPU, usually in crossfire-type mode, while doing something more taxing on your system like gaming.

You can try plugging in both monitors to whatever is your primary GPU and it should work just fine. Since you're using proprietary graphics, you should be able to look at the Windows help forums as well, since it will be a BIOS, hardware, and Catalyst issue.