There's an entire movement among music creators to move from analog to digital equipment. "Amp pedals" allow a guitarist to simulate the sounds of $100,000 of equipment with one digital box. Pocket synthesizers have done the same for beat makers, pianists, and producers.
Many of these new devices have one or two ways to output sound, through balanced/unbalanced 1/4" output jacks or via USB.
The current ADC solutions with a single 1/8" plug don't inspire much confidence for the analog path - but they also mean that the signal goes from analog>digital>analog in the creation device, and analog>digital>analog in Rasperry Pi+DSP+amp.
This Github issue was marked as completed but I think it's a valid feature request to make the USB inputs on a Raspberry Pi route to the DSP and connected Hifiberry amp. https://github.com/hifiberry/hifiberry-os/issues/208