There are 3 issues with T/Cs.
First are the # of pins. If the t/c has only 5 contact pins instead of the 8 that are found on the new Sony models, the SSM will not work, thus the lens will not focus.
Second, the Minolta AF system is programmed to autofocus only to f/6.3, with the exception of the 500/8 mirror, which overrides this programming. The reason for this is that because of the light falloff to the AF sensors as the aperture is stopped down, there is much more hunting for focus lock, which is hard on the entire system from batteries to motors and gears, etc. Therefore, a 2X t/c will only autofocus with lenses that have an aperture of f/2.8 and faster. Slower and you must manually focus.
Thirdly, the Minolta and Sony T/Cs will not physically mate to lenses other than those specified. While 3rd party "universal" T/Cs will mate to any lens, the KM/Sony design has a front element that mates tightly to the rear element of the lenses specified. While most lenses and third party T/Cs have recessed elements in these areas, the KM/Sony lenses have elements that are much closer to the mount's mating surface plane. In many cases, trying to mate these incompatable lenses and T/Cs will result in a glass on glass condition. Forcing the two together can actually physically damage these glass elements.
At least this is my understanding.