I cannot for the life of me get Eyefinity working on my PC. I'll list the setup below:
2x HD7870 in Crossfire
1 Phillips monitor (1920x1080) connected via DVI
1 Samsung monitor (1920x1080) connected via HDMI
1 Samsung monitor (1920x1080) connected via an Active Mini Display Port to HDMI adapter.
So far I can only ever get two of the monitors to work - Windows 7 recognizes all 3 but it won't work for more than 2 at a time. Catalyst Control Centre can detect the 3 monitors but when setting up Eyefinity it only supports 2x1.
The issue is most likely your adapter. EyeFinity can be picky about which adapters work (not as much as in the past though). I've never heard of a DP to HDMI adapter being used in the setup, normally most people get the validated apapters that are DP to DVI then use a DVI to HDMI cable.
These seem to be the best type of adapters, I use to run this one before upgrading to monitors with displayport. When I received the adapter the box even had the ATI/EyeFinity logo on it to show it.
Glad we were able to help, enjoy your EyeFinity setup. Once you've gamed on 3 screens, its hard going back to just 1. I'm playing Borderlands 2 now and for the sake of playing with friends I got it on PS3. (First game I've played on my PS3 since last October). While I love the game, it feels odd playing on just one screen, even though its my 46 inch LED. I've gotten so use to my EyeFinity setup that having such a limited field of view just feels odd now.