(Mini) DisplayPort conversion to DVI (or HDMI) may require an ACTIVE adapter. Converting it to Dual-Link DVI (or HDMI) requres a very expensive Dual-Link DVI ACTIVE adapter.
If you have two direct Dual-Link DVI ports I would cable them directly to your hi-res displays.
Then I would get an ACTIVE Single-Link adapter to DVI, and if needed, a DVI --> HDMI cable
I never got all 3 working, hence my wondering if it's due to it being a Flashed card, not official Apple.
according to AMD/ATI:
Connecting multiple monitors for AMD Eyefinity technology couldn’t be simpler. There are four easy rules to remember:
- The first two monitors can connect to the graphics card with any display output on your product: HDMI, VGA, DVI or DisplayPort.
- The third (or greater) display must be connected to the graphics card via DisplayPort.
- If your monitor does not have a DisplayPort connection, you will need an inexpensive active DisplayPort adapter for it. DVI to DP adapters can be had for less than $30 USD.2
- Every family of GPUs supports a different maximum number of displays.