The chips are somewhat of a matched set. Truthfully, while I"m not 100% sure, since the smaller one is labeled with the sound ID, I'm pretty sure it's the sound files. The larger one with the same numbering is used with multiple sound file chips, so I suspect that's the logic that selects what sound file to play based on either the serial data (command) or track offset voltage (conventional)
Yes, while you may get some function in a TMCC locomotive with a RS 5.5 or 6.0 board, they will only work properly in a Legacy environment.