MacBook Pro or PC soundcard

It is better than what you are suggesting though (an internal soundcard).

I've found that a Mac with Audirvana Plus and a decent USB interface is now very close to a disc spinner.

USB may have started off clumsily but that's the thing with PC audio. It keeps getting better. The async USB interface from Gordon Rankin and Nugent were big strides in getting to a good quality connection from PC to DAC. Most PCs are full of EMI and RF noise that affects the internal sound card.

Internal soundcards are susceptible to a lot of noise.

A USB DAC is a bit like a soundcard. It's just that the components usually benefit from better isolation from the insides of a PC, and usually have better power supplies as well.

USB-DAC with a good asynchronous USB Audio Class 2.0 implementation (not just USB 2.0).

Use BitPerfect if you use iTunes for your music library and enable Cache/Memory Play.

Better yet, use Audirvana Plus.

Use SSD and load up the RAM to as much as you can afford.

Actually most high end CDPs don't use SPDIF exclusively. A number use I2S or use their proprietary connections with separate word clock.

SPDIF can sometimes result in bad jitter control. FWIW, USB is really about sending SPDIF data over a USB cable instead of a regular toslink or coax digital but with async USB, there's some control over the clock.

*sigh*

USB is a PC based protocol. A transport is NOT a PC. On the PC, you merely use the USB connection to provide an isolated SPDIF/I2S interface (depending on the implementation) as well. Just that it is further away from the noise of the PC.

FWIW, Empirical Audio also provides a USB-I2S interface on their off ramp. If your DAC supports it, it is a better interface than SPDIF.

Yes USB is not perfect. It was not designed for audio.

But how could one get audio from PC? With an internal soundcard? That's an even worse solution due to the EMI inside the PC. With a PC's SPDIF output? That meant you used optical (higher jitter) or coax (higher EMI interference from the computer system)?

First generation examples of USB-SPDIF devices and USB-DACs were not great. But they did outperform many "onboard" soundcards that were susceptible to computer noise.

The second generation of USB-SPDIF/I2S devices like Wavelength's Wavelink HS and from Empirical Audio made an even bigger leap sound quality wise.

It would be silly to go back 3 generations to an internal computer soundcard.