Here is how you can use loops you purchased in studio.HD or Looptastic HD into meta.DJ:
1) Install the application you used to buy your loops onto your device.
2) Open the Loop Store and press Restore. You will need an active Internet connection. This will reload the loops you purchased with this app.
3) Wait for all the loops to download.
4) Open meta.DJ. Go to the Loop Store
5) Press Restore. meta.DJ will now download the loops you purchased on the other app that is on the same device.
Please note that the automatic file clean up in iOS 5 will delete your loop sets if you run out of space. This behavior is based on requirements from Apple that downloadable content can be deleted by the system. Please make sure keep at least 250MB free on your device to avoid this problem.