Decoupling of digital circuits requires a cascaded approach; multiple electrolytics (e.g. 10u) for distributed bulk decoupling. You want good quality, low ESR devices here; no real need for esoteric 'audiophile' caps. Each digital component should then have a local, small, ceramic decoupling capacitor (or two, e.g. 100n/1n). The intent is to stop HF digital noise getting on to the power lines. Each capacitor has a different resonant frequency range, where it is effective at decoupling; the smaller the cap, the higher the resonant frequency. The cascaded approach covers a wide frequency range.
The digital and analogue circuits should be well isolated in both layout and power supply, anyway. The digital decoupling helps reduce digital noise coupling back to the common supply point (e.g. single power transformer), and reduces radiated noise that might couple into the audio circuits.
The point where you need to start taking real care (to prevent digital noise injection) is in the digital interface to the DAC; both PCM stream and any digital control interface. The DAC clock, reference and output buffer are analogue circuits, and should each have their own local regulation and filtering, as should any external analogue processing after the DAC.
Check the DAC data sheet/app note for recommended supply and PCM/control decouplng approaches.
