Problems with 7850 and dual monitors on DVI/HDMI

Hey guys, I have a problem and I figured I'd ask here since OCN is unusually slow.

OS is Windows 8 x64.

I recently bought a used Asus 7850 DirectCU II, which has only one DVI port. I run two monitors, so this forced me to try hooking up one of them via DVI, and the other via HDMI.

For simplicity I'll refer to the monitor with the DVI cable as the "DVI monitor", and the one with the DVI cable as the "DVI monitor".

The first attempt was a horrible failure; the HDMI monitor said "check video cable" and nothing else showed up on the screen. However, Windows detected the monitor and listed it as working just fine. I also noticed a lot of visual artifacts and other weird glitches on the screen that was working. I unplugged the HDMI cable, and the visual artifacts remained. However, after a simple restart, they were fixed, and the one DVI monitor worked fine.

I figured the HDMI cable was just bad, so I switched it out. This time, both monitors showed the BIOS post screen flawlessly, much to my relief. However, when I booted into Windows, I was greeted with a whole new problem. While both monitors were now detected, the HDMI monitor had black underscan borders and was, for some reason, being detected by CCC as an HDTV. It also gave me a popup claiming that I'd connected a display that supports audio output, which is weird, because both of my monitors are HP 2311x's. They don't have speakers. On top of all this, the crazy visual artifacts and glitches were back. I decided to try JUST the HDMI monitor, unplugging the DVI one. To my surprise, after a restart, the HDMI monitor was working perfectly.

So the conclusion I've come to is that it's impossible for me to have a DVI monitor and an HDMI monitor plugged in at the same time, even though either one works fine on its own.

This problem only exists in Windows, though. If I just boot into BIOS, there aren't any artifacts or anything...the DVI monitor appears to be a little blurry compared to the HDMI monitor, but the screens certainly aren't flickering and flashing random colors all over. This leads me to believe that this is a driver problem...even though the problem exists on the 12.10 and 12.11 drivers, as well as the default Windows drivers.

If the card IS bad, I don't think I'll be able to RMA it considering it was purchased used. I'll have to return it to the original seller, which is just a waste of time and money  

My next step is to install one of my old 4850s that has a DVI and HDMI port. I'll try hooking up both of the monitors to that, just to rule out the slim chance that BOTH hdmi cables are bad (unlikely, since the one I have hooked up now is a known working cable)

Is there some rule I don't know about? Don't mix HDMI and DVI? I thought it would be okay since they're pretty identical, but I've had nothing but problems.

Thanks guys.