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.

USB is flawed. Why would you go from fiber to usb? You’re going backwards.

All dacs in preamps/integrateds are compromised compared to quality standalone dacs. 
It’s funny when people say don’t hook up a computer directly to your dac but every streamer is a computer.

There is only 1 streamer that has a galvanized input/output, and I use it with i2s into my dac.

@rbstehno stand alone DAC is my preference also since it isolates the conversion from both the computer's and the amp's electronics but OP is asking specifically about connecting his PC to the DAC in his integrated amp.

Ah.

"A streamer is a computer."

A single use box is totally different than a general use PC.

Galvanized, fiber optics, sales gimmicks.

+1 @travelinjack 

In addition to Foobar, you have the JRiver Mediacenter as another option for locally stored music. Connection from your computer to the Mac 7900 via USB A/B.

Using (for example) Quobuz as the source of music (PC app available), you can send the stream via USB to your DAC as well.

Give it a try. If you are satisfied with the soundquality, you will not need any additional hardware. If not, you may want to go with a dedicated streamer.

I am using an Android platform including USB Audio Player Pro going directly into the integrated amp via USB A/B (and as well via separate DAC to the amp).

It is all about personal preference.

Others have said it, but it is probably useful to summarize:

1) PCs are acceptable sources. Sonically the biggest issue with them is that they are not optimized for audio play back. They have inadequate DAC chips, they are prone to digital timing errors, capacitors are low grade, are prone to noise interference from the other functions of the computer, and other issues.
2) You need some sort of software program to manage music. Paid streaming services such as Tidal provide this. If you have music stored on a hard drive that you wish to play you need a program for that. Room is one service that helps you manage both in one space.

3) The OP has a DAC in his integrated amp and it surely will best the one in his computer. He therefore just needs to send the digital stream of the PC to the amp. The most common way to this is usb. Presumably the DAC in the amp offers other digital inputs but most computers tend to offer just usb as a digital output so his computer will probably be the limiting factor.

4) What is a streamer and should the OP buy one? Streamers are basically networking computers that have been optimized for sound. Some contain DACs. They also look like audio components.

The OP is obviously new to streaming. I am not familiar with his amp. McIntosh is a storied company. I can’t imagine that it would sound bad. Start there and stream from your computer. You may be so happy that you never feel the need to move on.

I used a computer into a DAC for several years before buying my first dedicated streamer. You can always upgrade later but since the OP already owns the amp and a computer it would be logical to start there

Travelinjack-I agree with you but some of the other posters are way off base. 
My server running Roon will never be hooked up to a dac. When I was using this Mac straight into the dac, the server was in another room and I used Ethernet to the dac.

All the Auralic/aurender server/streamers are computers, no ifs and buts about it. They run a proprietary version of some hacked Linux OS, big deal. I’ve done this before running Linux on a commercial server with commercial solid state technology (again using Ethernet to the dac) and there was no benefit to sound quality. IMO, the only benefit you will see is if the server/streamer claims they have an audio usb port, which some drool over. Me, I’ll never use it. You can buy thousands of $$$ of usb gimmicks/tweaks and it will still be flawed.

Who cares if a new Mac is running another task in the background. The new Mx processors run 38 trillion ops, so I don’t think it will slow down any. But, I turn off everything that is not needed during my listening sssions, after that I run my backups, etc.

You take a Nucleus that the vendor removed all diagnostic commands from the OS thinking that it will improve the sound. If it was running on 30 year old gear, that would be the right thinking, but not running anything in the past 10 years. Now nobody can figure out what is wrong with their nucleus, they can only guess which usually leads them to buying new hardware which might not be the problem.

I stream Qobuz from my ASUS Windows 7 computer to my DAC via USB. I have also ripped my CD collection (<4000) to uncompressed FLAC and I use Foobar 2000 to play those files. I kept all my CDs and play them regularly.

I have compared Qobuz playback to the corresponding CD (Jay's Audio CD3 MK III transport) and I can't hear the difference. I have also compared my ripped files to the physical CD and same result - no difference.

If the computer is doing something horrible to the sound it's beyond my ability to hear it. I suggest that you try comparing the CD to the streaming service you are using, assuming that it provides CD quality, and see if you can tell them apart. Just make sure you have carefully matched the levels.

Having said all that I am going to get a dedicated streamer one of these days but it's due to convenience instead of sound quality. I'm looking at an Eversolo DMP-A8 which will allow me to use a phone or tablet to control playing the content.

For whatever reason my experience is that digital sources don't have the range of sound quality of other components. I have 3 DACs, two transports, one vintage CD player, and a SACD player. I've compared them all and they sound very similar, if not identical. I realize that lots of people on this forum hear enormous, life changing differences, between streamers, internet switches, and digital cables ("The XYZ BLEW AWAY the ABC") but apparently I have tin ears. But those ears have saved me a ton of money.

@8th-note I am right with you on the not hearing any significant difference between my computer to the DAC and a much higher cost individual streamer/more expensive DAC combo. 

I read some posts on this site about the use of a DDC.  So I bought a DDC (Denafrips Iris) which I tried which was a greatly lower cost tweak. I believe (can't be sure because I can't AB test it like I did computer/old DAC vs. expensive DAC/separate Streamer) I am hearing some significant differences such as clearer more pronounced bass and some detail without the digital glare in the upper range. My belief is enough to feel that the sub $500 cost was worth it. 

@8th-note You can use a phone or tablet to control foobar2000 in your existing setup. This thread has a few suggestions.

USB. No one yet explained any physical concepts of "bad sounding" PC. You can use reclock/DDC if you are really concerned with "noise" coming from the PC.

Use HDMI.  It delivers bit-perfect digital audio to the DAC.  Only from the DAC to the speakers is quality an issue.  The data that goes into the HDMI is identical to the data that comes out of it, unless something is very wrong with the cable.