DAC connection to computer

USB.

But a separate streamer will sound way better. 

Don’t do it. You want remote control of your music without being tethered to a foul sounding PC that will not deliver "high quality."

Use your computer if you have a streamer in-between. Better if your streamer uses fbre optic cable.

I now have 3 of the Sonore OpticalRendu streamers and they are great. Especially if you want to use a cheap noisy computer like me in a different room (and floor)

There are a few opticalRendu being sold on the used market. My recent one cost me $200 + an EtherRegen,

So, what I am suggesting means DO NOT use the Ethernet cable (RJ45) into your Integrated amp. Instead use a streamer that can isolate your network noise and computer noise from touching your DAC. My opticalRendus takes fibre from a network switch ($70) and converts it to USB, which I assume your DAC supports.

Of course, DO NOT connect your computer directly to the DAC using USB. The noise from the computer gets into the DAC.

Connect directly from the computer to the DAC via USB.  That’s a good place to start to get you up and running.  Separate DACs and streamers can increase the quality by a good measure but no need to start with that. 

Connect directly to the DAC by USB from the PC. Use Foobar2000 as the media player and use Foobar2000 Controller Pro on a phone as a remote to select tracks and play.