Ah... I see... You are running the Mini's separately from your main system. Missed that in your earlier post, and I thought you were just replacing the fronts.

New plan: if you use the balanced cables to connect to the 2200's, use unbalanced cables to connect the 990 to the 7500 and switch those two channels of the 7500 to the unbalanced input. You'll need to recalibrate the system because the fronts will probably see a drop in signal strength of about 3dB when they change to unbalanced.