Well I played a little more early this morning and swapped out some more gear on the DK. I think his aggro issue was that he was undergeared compared to the rest of the team and so the locks were blasting them after a few seconds of blasting a boss. I upgraded his defense to now close to 518 (not doing heroics yet until I get him a little better geared) and so I did not open fire with my other toons for about 10 seconds and then kept a close eye on Omen to watch his threat, this worked fine. I also noticed a huge ooppsss, I had him specced unholy and so will respect when i get home