While computer-based audio offers many sonic and programming advancements over disc-based systems, it also brings greater level of complexity to a sound reproduction system.
As a reviewer, computer audio manages to be both easier and harder to cover. It's easier because you can, if you're clever, set up robust matched-level A/B comparisons between DACs and other components. It's harder because you have far more variables to consider in making sure all components are operating in their maximum performance range. Reviewing a USB 2.0 compliant DAC using a USB 1.0 pipe ain't gonna cut it.
When I first set up a USB DAC I try it with iTunes, Amarra, Pure Music, Audirvana Plus, Decibel, and even Preview. On more than one occasion I've served as in inadvertent Beta-tester. Recently I discovered an issue between Audirvana Plus and a USB DAC that caused the DAC to generate spurious noise when put into a software-induced mute mode. The manufacturer hadn't used their DAC with Audirvana Plus, so the problem was as much of a surprise for them as for me.
As a Mac user, one essential program is the Audio Midi Setup control pane. The Midi Control shows what audio devices are attached to your computer and what sample and bit rates they support. You can see current bit-rates and change them as needed. The Midi control also shows whether a device is muted and its current volume level. Many problems with volume, mute, or bit-rates can be easily solved with a couple of mouse-clicks in Midi control.
Another essential, but little-used program in the Mac is the "About This Mac" option, found under the Apple symbol in the left hand upper corner of your screen. Under "More Info" you'll see vital information about your USB chains that will show what devices are connected where and which USB protocols are being used with each one. The illustration to the right is the information pane from my Mac Pro desktop computer. If you look at the device list under "USB High Speed Buss" you can see that all three of the DACs currently connected are on the same buss. When I choose one, I can be sure it will get the same quality data stream as the others.
Although many computer audio products are advertised as "plug and play," the reality for a committed computer audiophile is there's no such thing as plug and play - even if a device seems to be working perfectly you have to check the details to make sure its operating optimally. For those audiophiles who have been avoiding computer audio because of this additional complexity, the bad news is I don't see this necessary level of rigor changing anytime soon. The good news is that most of the steps needed to insure optimal fidelity don't require very much time or physical effort - merely consistency. But consistency, especially in computer audio, requires constant attention to detail. But if it were easy, it wouldn't be as much fun...