Unfortunately MacBook Airs are not recommended for use with PreSonus devices. Even if it worked at some point before it may not continue to work reliably.
However, there are some things you can try.
First off, which FireStudio are you referring to?
If this is the original FireStudio (that says FireStudio 26 Input 26 Output) then unfortunately it will not work with OSX 10.11.
OSX 10.7 was the last supported OS for these units.
If you are using a FireStudio Mobile and are connecting via Thunderbolt you'll need to use the power supply that came with the Mobile as well.
If it's a Project (or a Mobile) you will want to try a full uninstall/reinstall of the drivers (instructions below).
If you try the steps below and are still having trouble with your FireStudio Mobile or Project please contact technical support.
Remove FireStudio family Driver Files
1. Disconnect your FireStudio Family interface.
2. The following list includes every possible file that may have been installed on your Mac, depending on which driver versions you have installed. If you do not see one of these files, do not be alarmed. The files are listed by location tree. For example, to locate the /Library/Preferences/PaeFireStudio.startup file, you will double click on MacHD and then Open the Library folder.
Delete the following from your computer (note some files will require that you type in your administrative password):
/Applications/Universal Control
/Applications/FireStudio Control Console
/Applications/FireControl
/Applications/FireStudio Lightpipe Mixer
/Applications/StudioLive
/Library/Application Support/PaeFireStudio
/Library/Application Support/PreSonus
/Library/Audio/MIDIDrivers/PAEFireStudioMIDIdriver.plugin
/Library/LaunchDaemons/tc.tctechnologies.PaeFireStudio.plist"
/Library/Preferences/PaeFireStudio.startup
/Library/Receipts/PreSonusUniversalControl.pkg
/Library/Startup Items/PaeFireStudio
/System/Library/Extensions/PaeFireStudio.kext
(If you are using OSX 10.11 El Capitan, 10.10 Yosemite, 10.9 Mavericks, 10.8 Mountain Lion or 10.7 Lion, the User Library folder is hidden.
Locating hidden Library folder on Mac
To get to it, with Finder open click the GO menu at the top, or control-click on Finder in the Dock, then select "Go To Folder" and enter: ~/Library. This is necessary for deleting the next 4 files)
/Users/YOUR USERNAME /Library/Caches/Juce/jucAppLock_Universal Control
/Users/YOUR USERNAME/Library/Caches/Juce/Universal Control
/Users/YOUR USERNAME /Library/Preferences/FireControlSettings.settings
/Users/YOUR USERNAME/Library/PreSonus
If you have other PreSonus products installed they may be shown in this folder. For the purpose of removing FireStudio you'll want to delete the following folders found inside the /Users/YOUR USERNAME/Library/PreSonus folder.
/Users/YOUR USERNAME/Library/PreSonus/FireStudio
/Users/YOUR USERNAME/Library/PreSonus/Universal Control (x64)
/Users/YOUR USERNAME/Library/PreSonus/Universal Control (note this folder may not show up on Mac OS X 10.9, 10.10 or 10.11 or later, that's ok)
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Remove .bom and .plist files
*If you've done the UC 1.7 uninstall script method above, and these files are not there, you can proceed with the next section.
Note: if you use OSX 10.11 El Capitan, 10.10 Yosemite, 10.9 Mavericks, 10.8 Mountain Lion, 10.7 Lion or 10.6 Snow Leopard, you also need to do the following:
a) Right Click the Finder
b) From the pop-up window select Go To Folder
c) Paste or type in this string: /private/var/db/receipts
d) In the folder that opens, find the files that have Universal Control in the label and move them to the Trash.
You are looking to delete these entries (they will be at the bottom of the list):
com.presonus.pkg.universalcontrol.bom
com.presonus.pkg.universalcontrol.plist
Repair Disk Permissions
(For version of Mac OS X 10.10 and prior)
5. Go to Applications > Utilities > Disk Utility
6. Select your system drive from list on the left
7. Click Repair Disk Permissions
8. Shut down your Mac once the Repair Disk operation is complete.
(For Mac OS X 10.11 - El Capitan, this screen has changed)
5. Go to Applications > Utilities > Disk Utility
6. Select your system drive from list on the left
7. Click First Aid
8. Shut down your Mac once the operation is complete.
Reset your PRAM
(After any removal of files as shown here will require all versions of Mac OS X to perform this function for the uninstall process to be considered complete)
9. Locate the following keys on the keyboard: Command, Option, P, and R. You will need to hold these keys down simultaneously
10. Disconnect all USB, FireWire, or Thunderbolt devices except for your keyboard and mouse. Turn on the computer
11. Press and hold the Command-Option-P-R keys. You must press this key combination before the gray screen appears.
12. Hold the keys down until the computer restarts and you hear the startup sound for the second time.
13. Release the keys. At this point, your computer should be completely zeroed out and you can reinstall.
Download and Install the latest driver
14. Go to http://www.presonus.com/support/downloads
15. Download the driver for you FireStudio family product from the PreSonus website.
16. Quit your web browser and any other application you have running
17. Double click on the downloaded .dmg file to open the disk image on your desktop
18. It should open a window with the installer package in it. If it doesn't, double click on the PreSonus Universal Control disk image on your desktop
19. Double click on PreSonus Universal Control.pkg to launch the installer
20. When the installer launches, click “Continue”
21. Click on the icon of your Internal hard drive and click “Continue”
22. Click “Install”
23. When the installation has finished, click “Finish”
24. Reboot your computer
