The combo inputs are mono line inputs, so you need to use two input channels. You have the option to link input channels (1+2, 3+4, 5+6 ...). The Series III mixers can handle "heavy" inputs. Simply go down to 2 or 1 dB with the gain knob. If you experience some hum or noise, a DI box with Ground Lift will help. Generally it doesn't need DI boxes, but using them is a more professional approach, because the signal is balanced and you can use the XLR inputs, which have a wider gain range.
The mixers allow patching of inputs channels. An input on channel 16 can be routed to channel 1, for example. You can also route an input signal to several channels.
