All I think I know is that a company is developing a VST plug-in that can deal with Auro, and therefore could be used with MC. It might not be cheap, and might come bundled in a hardware package. Another member here may have better details, but I'm not sure if there is an NDA or not.
As for Atmos, it's still in the very early days. There are definitely no open source decoders, if decoders is even the right terminology to apply here.