If you were playing redbook (44/16) cd quality files (AIFF) from your MAC, I believe it to be likely you would hear a benefit from the USB converter. Can't say about MOG. I believe coax to be superior to optical spdif connection. Would not use an optical to coax converter over a straight coax connection unless EMI/RFI interference was a problem.
Quality cables make a difference. Need not be the most expensive. Budget end audioquest or wireworld (only 2 examples, there are others) perform well.
Which AL pre do you have?
Quality cables make a difference. Need not be the most expensive. Budget end audioquest or wireworld (only 2 examples, there are others) perform well.
Which AL pre do you have?