I can confirm that since posting the DXDiag I realised that BIOS 46 was released and have duly updated the BIOS to the latest version (dated 4th July 2013, however not uploaded until after the 8th July 2013 and therefore had not been installed)
It would obviously be immensely useful for you to know I have also noted that the issue also occurs outside of Windows and exists at the initial BIOS boot sequence. I have noted that at times the monitor states it does not have any signal when initially booted and one has to turn off the computer, turn off the monitors and then turn the monitors back on and boot the computer for the initial BIOS splash screen to appear on both monitors.