The MT 48 driver supports up to 32 input and 16 output channels at sampling rates of up to 48 kHz. 
At higher sampling rates up to 96 kHz, the number of channels is reduced to 16 input and output channels each. 
At the highest sampling rates up to 192 kHz, the MT 48 driver can process up to 8 input and 16 output channels. 
Under SETTINGS USB I/O you can select which channels are sent to and received from the computer via USB. The channel numbers are assigned dynamically.

Be aware, that the MT48 MacOS driver can reduce the number of USB channels in the Audio MIDI Setup menu. If you see a limitation on your MT48 to not use all these up to 32 input channels please check, the audio device driver settings.