Balance the ductwork system would be where I would start. Also, adding supplies won't help without adding returns--how many return grilles were added to the new MBR/family room?

No additional returns were added! The 2 contractors who visited last summer during construction were indicating another unit was required at a cost of $8k!!

If it is an older ranch style house, then you really need a 3.5 ton unit to take care of all the 2000 square feet that you have. You can still use one system even with an upstairs and a down, but you will have to get a zone system installed to condition these spaces well enough. If you get a heat load calculation done on the house, then you might find out that your 3 ton unit will work on the house, but the ductwork will have to be reegineered to accomadate a zone system.

Thanks all for response! Seems the issue revolves around the duct work, balancing and zoning. Seems the contractors I have spoken to so far are intent on adding a second 2-3 ton unit outside and a second air handler.

Any additional ideas??

Thanks!

I would say if the ductwork was modified properly and a return grille was added then the system would work ok but not great. You didn't say where you live but the tonnage might be light for the new size of house. Is the family room and mbr at the opposite end of the house as the air handler?
You didn't mention how the heating works.

Thanks. The house is heated separately via hot water baseboard so the only duct work is for the AC. The house is in northern NJ. The MBR is built on top of the Family room and those additions are perpendicular to the main rectangle of the ranch house, forming an L. The air handler is in the original house attic, near where the addition(s) are.