rekordbox with MOTU 624 issues

On a High Spec MacPro with a MOTU 624.

rekordbox runs fine with Internal Audio but won't run audio when the MOTU 624 is selected.

recordbox seems to see the 624 because it knows that the labelling is different.

Tried different sample rates etc but nothing has worked.

Done all the switch it all off and on stuff but still no audio.

It actually stops the program from loading waveforms in the player as well.

Anybody had an issue?

Thanks