No difference in sound quality or internal processing: every iLive Mix Rack can mix 64 Inputs down to 30 Busses with 8 Effects. The only difference is in the amount of physical Inputs and Outputs each Mixrack has. I’ve mixed shows of over 40 inputs at FOH on an iDR-16 when it was receiving those Inputs (via ACE) from my iDR-48 monitor rack.