I don't think there is any such thing as a 100% solution. Kind of like reaching absolute zero.
Let us know the results of your audit?
Equipment sounds grossly oversized. This leads to short cycling, which means far areas never receive conditioning. Does your ac ever run continuously?
A mini split works great in small spaces, if duct constraints make one unit impractical.
Hopefully this free audit will give you an analysis and recommendations regarding the improvements you hope to make. Please share.