Make your own chunks, and the algorithm easily becomes embarrassingly parallel. Give each of the 100 cores 1 GB, let them run independently, and don't sweat the few bits of compression efficiency you might lose. If Amdahl's Law comes into play, it's because you're constrained by memory or some other I/O system rather than the CPU core.

Decompression may not be embarrassingly parallellizable for an existing algorithm, if it relies on state that persists through every bit in the data set. But a codec algorithm can be designed to be embarrassingly parallel for both legs.