They are different.. to use AVCS heads you would need the wiring harness and ECU that goes with the later model heads.
Aside from the massive cost and hastle involved with trying to get later model 2.5L heads to work correctly on your car, the ej205 heads you already have flow more and are therefore capable of producing more power than 2.5L heads.
The combustion chambers are also different. Like you mentioned, you can deal with the increase in compression ratio by going with a lower compression piston (or thicker head gasket).. but the best way to deal with it is to have the combustion chamber machined out a little to closer match the 2.5L combustion chamber. Going the piston route does correct the compression ratio, but it does nothing for the steep step in the combustion chamber itself which is thought to cause hot spots and detonation in the cylinder. If you want the best performance you can get out of it you're going to need to rework the combustion chamber to some degree.