You will want to first load a virtual instrument into Studio One 3, enter some MIDI notes into the Editor manually, and verify that your audio device is configured properly in the "Audio Setup" window. Once you verify that you have audio in the program and that your samples are loading, you can then move on to troubleshooting your MIDI device.
You should first go into your External Devices menu and verify that you have the correct ports set for sending and receiving MIDI data. You can then open the MIDI monitor by clicking the icon of the 5-pin MIDI cable at the bottom left-hand corner of the screen. If you are receiving MIDI messages from your device, the answer may be as simple as going into the Inspector window by clicking the icon of the letter "I" at the top left-hand corner of the screen. In the Inspector for the track that you are working with, make sure that you are using the Akai MPK. If the MIDI data is not showing up in the MIDI Monitor, you will want to follow the below instructions:
1. Go to Help>Open Settings folder.
2. Copy the contents of the folder over to a folder on your desktop.
3. Close S1 and delete the contents of the settings folder with the exception of the user.license file.
4. Open S1 and go to Studio One>Options (Preferences on a Mac) to reconfigure your settings.
*If you are missing presets or Sound Sets after doing this, simply double-click one of your Sound Sets under Documents>Studio One>Sound Sets.
5. Continue on to the next step for configuring your MIDI device.
6. Open Studio One and go to Studio One>Options (Preferences on a Mac)>External Devices.
7. Choose to add the device as a new keyboard if you are using it for note entry, a new instrument if you are using the device to send MIDI to the device as an instrument, or a new controller if it is a control surface or you are going to MIDI map the device for use as a controller.
8. Choose the correct MIDI port from the "Receive From" drop down. You only need to use "Send To" if you are sending MIDI to the device and you have set it up as an instrument instead of a keyboard.
9. Do NOT select any of the MIDI filters as they will filter MIDI data.
10. Make sure that you check the box to set your device as the default instrument. If you are using multiple devices, you will need to select the device from the "Control" drop-down at the top left-hand corner of the screen with a song open.
11. Create an instrument track with a Presonus instrument, arm the track, go to View>Editor to open the MIDI editor, and press the record button in the transport to begin recording.
If you continue to have an issue, you may want to reach out to Akai for information on drivers, compatibility, etc.