My MacBook Pro doesn't work with my Marantz hooked up with a 3.5mm to RCA cable. Oddly, my phone and Android tablet work fine. I haven't tried my iPad Mini yet.
It could be a setting in your computer, or it may be that the output jack on the computer is defective. It would be good to try hooking it up to other things to see if you could get it to work with anything. For checking the settings, going to a site devoted to Mac computers should be the place to get good advice on how that should be done.
You know the Marantz input works because you have used your phone and tablet with it, so that can be eliminated from consideration. It is obviously something about the computer, and if I were to hazard a guess, I would guess that you have some setting wrong. Though, again, it is also possible that the output jack or connection to it is defective, so it could be a hardware problem, but most of the time with this sort of thing, I think it is a software setting that is the problem.
