For Hi Fi music source you have your standard hi fi digital outputs that have been around for years:
Coaxial
Optical
For the amplification you have your standard hi fi analogue inputs that have been around for years:
Balanced
Unbalanced
So for traditional Hi-Fi. The Dac is the part in the middle of the source and amplifier that plugs into the above connections and turns the sources digital 0s and 1s into waves that the amplifier can amplify. You just have to make sure the DAC has the correct type and number of inputs and outputs that you require. Apart from that its the usual listening to see if you like the sound.
The computer only introduces new inputs ton consider. Firstly a computer may or may not have the traditional Hi-Fi digital inputs. If it does then you can just treat it like any other hi fi source. If it doesn't then you need a DAC that has a computer type of input. There is one common and two not so common computer inputs on DACs. It is perfectly fine to choose this option even if you computer has traditional Hi Fi outputs.
USB (the common one)
One benefit is the increased number of sources you can have with a CD player like quality DAC to play stereo:
Computer
TV
Blu Ray
Set top box
Portable MP3 player
A second benefit is that it may upgrade the DAC quality compared to an old or cheaper CD player. The CD player would then be used as a transport only and you would connect the digital out to the DAC rather than the analogue out from the CD player ot the amplifier.
A standard computer setup would be (in my case):
Computer playing music with a music player such as iTunes, Foobar, MediaMonkey. (mac mini, itunes)
A digital cable such as optical, coaxial, USB. (USB)
DAC. (rdac)
Analogue cable. (atlas hyper)
Amplifier. (cyrus 8vs2)
Speaker. (Spendor)
There is one complexity with a computer, and that is making sure the music is sent out in the musics format and not converted by the computers mixer. ie for CD rips making sure the rate is set to 44.1khz. It isn't that complicated but I would google it once the setup is working fine, as how to do it is operating system & music player specific.