I have done similar project on Arduino Uno (with less channels & quality) and based on that experience 100MHz DSP should easily be able to do this,
With a 16MHz processor???
Even the Due only runs at 84MHz.
I can code the DSP with C/C++ or assembly for performance.
To code an efficient DSP algorithm you need architecture that is suited to the task, using general purpose architecture like on the Arduinos can never be efficient.
All the mixed channels are digital and the sample data for the channels should reside in external memory because there can be several MB's of data.
That rules out the Arduino.
I simply can not see where the Arduino would fit into what you want to do.