I wouldnt have traded an asus board for an msi in the first plance.
Try to direct a fan to blow on the northbridge heat sink.
You could always buy a bigger passive heatsink and attach it to the mobo like the zalman ZM-B47J. This could also be a problem it could block your graphic card from inserting. So take some measurements and think this carefully.
If you dont care about your warranty you could always do something like what I did
This is the ASUS A8N32-Deluxe mobo with two blue heatsinks glued to the northbridge and soutbridge. It reduced the temps a lot.
I got this mobo for cheap and it not under warranty any more so what the hell.
You will notice there is no graphic card in there. Actualy there is just it's an pci one. I use this pc as a part of my render farm.