trouble with mixer connected to logic

Hi i brought a firewire alesis multimix 12 a few months ago to use with logic 8.
It works absolutely fine recording into logic but the audio coming from the mac doesn't come through or even register on the mixer. i've tried everything i can think of but nothing's worked, i'm hoping someone here might be able to give me a few tips...

Have you chosen the Alesis as your sound output device in System Preferences? Its default is Mac's Built-In Output.

yeah, i've done all the obvious things.

I believe it's simply not an output device, my story is I had a multimix 8 firewire I tried connecting it to mac osx and it wouldn't show up as sound output. The field was grayed out.