JMarley, I am afraid that you don't understand, or I don't understand what you are saying. The McIntosh MA5100 is an integrated amplifier, meaning it has a preamp section and an amp section. The preamp section has inputs for outside sources, a turntable, a tuner, a tape deck.
The phono jacks are for input only and are not to be used for feeding a signal out. The phono jacks are also ONLY for a turntable. The othe inputs are what are called "Line" inputs.If you had a tuner you would connect it here. If you connected the tuner to the phono input the signal would be too strong and possibly harm the amplifier.
Now you have a receiver, a pioneer SX850, and it has its own set of inputs and outputs plus it has a tuner. If you wanted to use the tuner that is in the SX850, you could take the tape out connectors on the Pioneer and hook then to the tape inputs on the Mac, but the SX850 receiver's other sections would be wasted. Tis a far far better thing to get a tuner and connect it to the tuner input on the Mac and use the SX850 in another room with a pair of its own speakers.
Does this help?