Newb to DAC question. Benefit of a DAC for only CD listening

Hey J200jr. Keep your NAD516 and get a Bluesound Vault 2. You could rip all your CDs into the Vault via hi-Rez Flac files AND you will have the ability to start streaming music. If you want to try Roon, or Tidal or any new service.... you can explore. Also I think the DACs inside are great and try MQA files too.
If you are dead set on getting a better DAC, look at the Schiit Bifrost Multibit.
One of the cool things about Schiit Audio, is that they offer board upgrades when the technology improves. Offering their customers the chance to upgrade at budget prices. But if you want to try MQA, those guys stated they are not going to offer that technology with Schiit products.

What is the rest of your system?

I believe that unless your CD player is a weal link in your system, using it as a transport into a budget DAC may not provide any sonic improvement. That is not to say that the sonics may not be changed, but that change doesn't always make for an improvement. 

What about the sound of your system are you trying to improve?

That cd player is fine. In this case, don't waste money on an outboard DAC.

or an Oppo 205 - send it back if it doesn't sound better...

another avenue to explore is some isolation devices for the USB interface