for example, I would like to know if there are ADCs with a output buffer not unlike a fifo buffer that allows the connected mcu to transfer the data in bulk and perform other tasks while the ADC is preparing the next batch. You could do that with a DMA to transfer ADC samplings to a buffer without core clock cycles.
Unless you have one MCU for one ADC channel, the 60 ADC samplings will not be processed exactly at the same time.
If you transfer data thru an USB 2.0, data rate can be really fast > 849 KBytes/s with an arduino DUE.
With oversampling ( times 256) and some lines of code, you can obtain 16-bit ADC samplings from 12-bit ADC samplings. Since a DUE can sample up to 1 Msps, you could do that with only 
20 DUEs for 60 ADC channels... Good luck