i can't figure out how to set up an audio instrument and midi instrument to run simultaneously

Hi

Simply create extra channel strips using the action menu top right of the strips area (at Patch, Set, Concert level as required).

With Software Instrument and External MIDI channels, make sure that you have the correct "keyboard" input selected in teh Channel Strip Inspector.

CCT

If you start from an instrument based template vs. midi based, you will have to assign the incoming midi signal to a controller before the channel strip will allow you to select your controller for the input. In the assignments & mappings area, look for midi destinations with a subheader labeled as Notes with a value of 1-16. (1-16 are the available midi channels.) Click on Notes and it will open a pop up to define the midi input. Pick your controller from the list of midi devices and assign its input to the midi channels you would like to transmit on via the controller. Once you take care of that, add a new channel strip and select the type as instrument and you should see your controller listed in the input box. Create the channel and then highlight it on the mixer and, finally, assign a midi instrument to it from the assignment screen.