With the iRig 37 connected via USB, you will need to open Studio One > Options/Preferences(OS X) > External devices, and create a New Keyboard, with the MIDI "Receive From" assigned to the MIDI port the device is connected to. You don't need the MIDI "Send To" set. Also, Don't check any of the MIDI filters, only check filters if you want block a certain MIDI message.
If you require further assistance, please create a support ticket to discuss this in more detail.
We also encourage you to create a thread about this on the Presonus user forum.
https://forums.presonus.com/viewforum.php?f=108. This will allow for back and forth discussions about an issue or question and more points of view as to possible different approaches or workflows.
