are you sure you mean 6.1? That I believe is a Mitel release. You should check with their support.
If you are not dependent on the Mitel blades then you should consider 7.1. Otherwise Mitel has made 7.x available for their blades (excluding 6040).
Quite frankly with the HW config you put down, I'm surprised 6.x worked at all without mod. Others will know better.