Are you using the mini Display Port to drive both your monitors?  

I'm using the two HDMI ports.

You may want to contact Visiontek to confirm. They make the board.

There is no mention of the display specifications for that board is capable of what you want. Dell may have been thinking you only wanted 1920 X 1080.

A similar board https://www.visiontek.com/graphics-cards/visiontek-7750-3m-4k-uhd-three-monitor-graphics-card-detail.html#display-specifications shows that the HDMI for this graphics card is 4K capable.

This was my request (I already had two 1920x1080 monitors):

"I would like to upgrade my video card to drive two 2560 x 1440 resolution monitors."

I think I found the manual on the visiontek site under product category "7750 HDMI Audio". 

It says

"Supports 2xHDMI(1.4a) port and DisplayPort 1.2 @2560 x 1600 resolution"

I'll pursue this with VisionTek and report back.  Thanks for pointing me in the right direction.

Yes, please update when you hear from VisionTek.

Woot!

After 3 hours of reinstalling drivers and Catalyst software and rebooting and fiddling with conceivably relevant video-related settings and swapping monitors, I got a cryptic message that "an HDMI to DVI connection was detected".  I had two HDMI connections, so that was odd.  I pulled one of the HDMI connections and used the DP connection instead.  Now I've got 2 2560x1440 displays.

Thanks for your help.

Excellent news.

So are you running DP to DP or DP to HDMI?

I would still be interested to know whether dual HDMI was possible.

The card is suppose to support 3 monitors.

One monitor HDMI to HDMI.  The other DP to DP.

I did manage three monitors before, but it dropped the resolution of all monitors to HD.

Final update.  I got an email from VisionTek this morning saying I should update my drivers, and they forgot to include a link.  I asked for the link.  Of course I'd done driver update from within the OS, but this prompted me to search on their website.  I uninstalled the old Catalyst and installed new Catalyst + drivers.  Then I got an email with a completely different driver page and completely different software on it.  Uninstalled again and installed the completely new software from the new link.  All was well.  Then I switched to using two HDMI-HDMI cables and everything looks good.

That's a lesson learned for me.  Hit tech support early and often, I guess.  There's lots of cruft on the internet.

This is the link sent me by VisionTek support:

http://support.amd.com/en-us/kb-articles/Pages/AMD-Radeon-7000-Series-Drivers.aspx

Excellent news.

Yeah, AMD is the maker of the actual GPU.

HDMI cables do not like resolutions beyond 1920x1080 at 60 hz refresh rates. At the higher resolutions the refresh rate can drop below 60 hz. What refresh rate are you getting?

No. The different versions of HDMI cables are not that much different. Some will do better than others, but most can't do much more than HD. 2560x1600 Is about twice the pixels of HD so the video card will decrease the refresh rate to around 30. Some will notice flickering at this rate, and games could run poorly. That's why Display Port is needed.

If the HDMI cables are 1.3, shouldn't they be able to support 2560 x 1600 at 60 Hz?

But if the graphics card claims to support HDMI 1.3, isn't it required to output 2560x1600 at 60 Hz?

That is the HDMI specification.

I can't speak to the specifications, but I'm not running that higher resolution because the monitors max out at 2560x1440.  My refresh rate is 60 Hz.