Audio line-in problems from interface to computer

Hi,

I'm trying to digitally record a keyboard through an interface using my Macbook Pro.

Here's my setup: I have a Juno-GI Keyboard with a cable connecting its output to the input of a Boss ME-70 multi-effects board (my interface). Then, I've connected a cable from the output of the effects board to the input of a 13" Macbook Pro (through a 1/4" to 1/8" adapter).When I go to System Preferences and set the audio port to "input," the "line in" option appears, but the meter does not pick up any sound.

I can, however, connect the keyboard directly to the computer, and it does pick up sound.

Is the interface incompatible with the computer? If so, what can I do? I really want to record with the effects that the interface allows me to use. And if they are compatible, then what am I doing wrong?

Thanks,

Jeff