The audio interface has it's own power supply and is connected to my laptop via firewire.
Unfortunately my laptop's battery has died so I always have it plugged into the mains supply too.
On top of that, I have two monitors that are both connected to the mains & to the audio interface's main outputs.

So, I guess I'll try a DI box. Can you recommend any

Thanks for your help guys!
Pete

[Non-text portions of this message have been removed]