I'm writing this on a 2560x1600 Dual Link DVI monitor connected to a computer using HDMI 1.4.
Stop searching for HDMI to DVI-DL adapters. All adapters that you'll find are passive single-link adapters, even though they may be advertised as dual-link.
Although a HDMI 1.4 to Dual Link DVI adapter is possible to implement using an Analog Devices
ADV7619 297 MHz HDMI 1.4 receiver that does automatically split high pixel clock links into odd and even pixels and two
ADV7513 165 MHz HDMI 1.4 transmitters to transmit the pixels over two separate links, no manufacturer is making such a device.
You need a device that generates Dual Link DVI output from a single link input. And the only one that's widely available is a
DisplayPort to Dual Link DVI adapter, sold under several different brands.
With that, we've reduced the problem to converting HDMI 1.4 to DisplayPort 1.1. There were no solutions for this until recently, when the STMicroelectronics chip
STDP2600 became available. Several brands sell adapters based on this chip. In case your monitor takes a DP input at full resolution, using only this adapter is enough - no need to convert to DVI-DL.
Connecting those two together should provide a HDMI 1.4 to Dual-Link-DVI solution. However, the Linux Radeon driver (xf86-video-ati) was still not happy with it, and ignored the 2560x1600 videomode in the list of valid modes in EDID. The reason was that the Linux Radeon driver would enable pixel clocks above 165 MHz only in case a monitor has a HDMI Vendor Specific Data Block in the Consumer Electronic Association extended block of EDID.
Obviously, a pure DVI monitor will not have a HDMI VSDB in CEA EB of EDID. I solved that by adding a S/PDIF audio de-embbedder for HDMI that I got off eBay into the chain that adds the CEA EB to add audio descriptors to EDID. A proper solution would be to provide a modified EDID file directly to the driver.
This works for Linux, on Windows you may not need the EDID change, or you may need a more extensive one. I don't have a Windows machine to test.
String all three together, make sure all are powered up via their USB connectors and voilà, beautiful full resolution 2560x1600 picture at 60 Hz refresh rate on my Dual Link DVI monitor.