Just as an update, i had contacted Seasonic to ask them the best way to test my psu and to see if they had any solutions to my recent issues. Here is the response and i must say it was a quick one (within 24hrs)
Hi Andy,
Many of the DFI board have +5VSB start up surge of over the Intel specification of which our power supply reads as a faulty mainboard and therefore can cause restart and boot problems.
We have customers who have returned their boards to DFi for an upgrade and then problem solved and therefore I suggest that you contact DFI and have it upgraded to one of their newer boards.
Has anyone had any expirence of this and does it sound right? To me they are saying that there psu's done work well with my board?
Cheers