Toojays, you are correct regarding the stated maximum resolution, as mentioned in my post 18/6/11 3:12 above. In other words, Dell has stated in its documentation that the maximum possible resolution via HDMI is 1080p (i.e. 1920 x 1080) which is what has caused a lot of the confusion.
You should be aware that HDMI and DP are simply methods of communication and as such, there is no reason why HDMI should be restricted to 1920 x 1080 when DP can be used to display 2560 x 1440. Consequently, some people understood that Dell had somehow restricted the input of the HDMI port; however, Dell subsequently confirmed that the U2711's HDMI port is passive and does not restrict the input signal.
You can be assured that IF your graphics card and driver can produce 2560 x 1440 via HDMI (and your cable can transmit such a signal over HDMI) that the U2711 will be able to display 2560 x 1440 at 60Hz and 32-bit colour via HDMI (i.e. as it can via DP).
The easiest way to select this resolution may well be via the control panel for your graphics card where you create a custom resolution. This did not always work for older drivers; however, the more up to date drivers are capable of creating and using this custom resolution. I understand that some people have been able to edit the EDID file, which presumably is just to add 2560 x 1440 to the list of selectable resolutions; however, I can't really comment on that further.
The following may prove useful reading if you require further information http://forums.whirlpool.net.au/forum-replies.cfm?t=1479962. Much of the commentary on editing the EDID file is towards the end of that thread and there are other links there too.
As for wanting to use HDMI instead of DP, I don't see the reason for this. DP can provide the same functionality as HDMI (i.e. it can transmit audio) so perhaps your problem is with your audio settings.