USB

If you're serious about audio you just plug a cable into your breakout box and have your interfaces. converts, and preamps there. Your sound hardware can be anything from a pure i/o to an elaborate instrument under computer control. You can do audio synthesis and compositing on the CPU, GPU (not so different from a DSP) or external hardware.

Soundcards are only 'gone' in the sense that PCI cards are less important because many people use laptops and the audio built into motherboards is more than Good Enough for everyday purposes.