Focusrite Liquid Saffire 56 problems on brand new iMac

I have a mate who's just shedded out over £2000 on a brand new 27-inch iMac and another £500 on a Focusrite Liquid Saffire 56 audio interface only to find that after about 20 secs the audio completely drops out. He's a music producer so it's really important that the problem is fixed. In terms of the setup, the Liquid Saffire is connected with a Firewire cable which passes through a Thunderbolt to Firewire adapter and plugs into the iMac.

May I reitorate that both the iMac and Liquid Saffire are brand new. I think it's down to a dodgy Thunderbolt to Firewire adapter, however it may be to do with Mavericks or something else.

Any thoughts?