The official zynthian kit has 2 audio inputs and 2 audio outputs. It supports multiple inputs and outputs but you must implement this yourself. This can be done with USB (like the TASCAM US-1608, Behringer UMC1820, etc. - I have both of these) or you could use I2S boards like the HiFiBerry DAC8x. (This does not support audio input which is a real boon for zynthian but can be expanded with their ADC8x add-on.) Or, if you are willing and able to do some engineering, look at this thread where we designed and build a prototype multi-port I2S audio interface. I want to see that project progress but do not have the bandwidth to advance it myself. I hope that @stojos is continuing with its development. (I would love to see a single board that has 8 inputs and 8 outputs available for zynthian but I don’t think that is the direction that @stojos is taking.)
So yes, zynthian can have multiple inputs and outputs but to put them all in one box requires some DIY effort from yourself. (I am building a flightcase with 8 input, 16 output zynthian using TASCAM US16x08, RPi5, 5" touchscreen, PSU, etc.)