I,m not 100% sure about this ,but it may help.
A320's have FADEC which involves no mechanical linkages whatsoever. The whole issue is electronic. It also speaks directly to the flight management systems.
757's have an EEC system. The throttles are still directly linked to the engines and the EEC function is to control a stepper motor in the fuel flow governor to trim fuel requirements more accurately.All auto throttle functions are still fed mechanically into the linkage system.
With a FADEC engine autothrottle is part of the FADEC!!!!
Hope this is of some use.