bpfergu :
Pinhedd :
I just saw your edit, HDMI and Single-Link DVI do not provide enough bandwidth to drive anything above 1920x1200. 2560x1440 and 2560x1600 can only be driven by Dual-Link DVI-D or DisplayPort.
Are all three of your 27 inch displays identical? My understanding is that the 290 and 290x have each one Dual-Link DVI-D, one Single-Link DVI-D, one HDMI, and two mini DisplayPort.
All 3 monitors are 27" QNIX 2560x1440 and only have a single DVI-D output.
The 290s have 2 dual-link DVIs, one HDMI, and one display port. So it sounds like I will need to hook up the third monitor via the display port.
Would this item suffice?
http://www.newegg.com/Product/Product.aspx?Item=N82E16814999030
Ah yes, 2x Dual-Link DVI-D makes sense. The Dual-Link DVI-D has enough bandwidth to drive the display, but the HDMI port does not. With that said though a 2560x1440 display should still work on a Single-Link connection, just at a lower resolution. My suspicion is that all of the TMDS pairs are being gobbled up by the two Dual-Link DVI ports when they're running in Dual-Link mode. I can't find any documentation to support this so it's just a hunch.
Do you by any chance have any Single-Link DVI-D cables lying around? Perhaps from an older display? If you do, try swapping one of the Dual-Link cables with that one and see if the third display pops up. This would indicate that the TMDS outputs can be configured as Single/NC/NC, Dual/NC/NC, Single/Single/NC, Dual/Single/NC, Single/Dual/NC, Dual/Dual/NC, Single/Single/Single, Dual/Single/Single, or Single/Dual/Single, with those being the link speeds on the DL-DVI-D-0, DL-DVI-D-1, and HDMI ports respectively. NC stands for No Connection. What you want to configure is Dual/Dual/Dual, but are limited by the number of TMDS pairs in the HDMI cable to Dual/Dual/Single but that doesn't seem to work. This would seem to indicate that there are at most 12 TMDS pairs available; Single-Link DVI-D and HDMI require 3, and Dual-Link requires 6. I'm going to dig around for some documentation but I would appreciate it if you could test this for me.
EDIT: That adapter is only DisplayPort to Single-Link DVI-D. Here's one that supports Dual-Link DVI-D output
http://www.monoprice.com/Product?c_id=104&cp_id=10428&cs_id=1042802&p_id=6904&seq=1&format=2