Types and reason to use of not

The USB port on the back of the turntable is to transfer the signal to your PC or MAC. It requires a cable. I assume when you plug in the turntable into a computer and turn on the TT, a window should pop up asking you if you want to play the record or store it.

The port on the front of your Marantz is to plug in thumb drives.

Optical connections are nearly always inferior to coax. So use coax for both connections.

@gregchick0

are optical outputs of my 6006 CD player better to use to my preamp than the RCA, or are the Coaxial ports better to send to the preamp?

Not meaning to be rude, but why not join the club, and try each, and let your ears determine which sounds best to you. That’s pretty much what all of us here do. What sounds best in your application could depend entirely on your components.

You have to read the directions for each piece of equipment.  USB ports are often for maintenance--adding a firmware update.  I remember one Streamer that I really wanted to use a USB out and the usb on the back was for firmware in.  

So nobody here knows the answer to all these quetions.  Generally you can now google the manual for a piece of equipment. You can figure it out.

Jerry