you could try to set the latency to 512 and you should always have enough free space on your device.I would say at least 1-2 GB.Cubasis sets the latency automatically to 256 but you could just fire up another app before you launch cubasis.I.e you can start audiobus before and set the latency to 512 there.Or you can start Nlog which sets the latency to 512 automatically on iPad2.Start cubasis then and shut down the other app.Now cubasis is set to 512.