Hi,

It's beginning to look like you may have a faulty line out from your KN1400. If you can record from the headphone output you should be able to record from the line output. The only other possibility (assuming you are using the same cable in both situations) is that the line input impedance on the Mac is too low to work with the KN line out (even so you should still get a very low volume recording).

Cheers
Len C.