The following issue was discovered when attempting to use MOTU 828 and 896 with FinalCut Pro in OSX. However, it is not limited to MOTU Firewire interfaces.

There is a bug is in Sound Manager, which is currently incapable of supporting more than two channels of input. The crash will be most common in Apple applications, like iMovie and FinalCutPro that use Sound Manager for audio. Nearly all other audio applications will directly support CoreAudio. This issue can manifest with any audio hardware that delivers multi-channel audio input under OSX.

Apple is currently working to update Sound Manager to support multi-channel audio input. Since the issue is particular to Sound Manager multi-channel input,
you can potentially workaround the issue by disabling the the multichannel audio hardware's audio input (in the Audio MIDI Setup).