Preliminary parts list:

 - WM8804 S/PDIF receiver on input
 - TAS3108 DSP
 - 4xWM8804 S/PDIF transmitters, or... maybe cheap and great DAC chips too... Maybe the PCM1798 + cheap I/V and filter stages? Could be upgraded, can sound nice even in cheap surrounding, and could sound good surrounded by better components...
 - ADuM/ISO chips between DSP and DACs to detach DSP's noisy ground from DACs.
 - 24C512 EEPROM to store DSP's firmware
 - Arduino? To burn the EEPROM, control Wolfson tranceivers, and for further use - switch precalculated biquad filter values during source's sampling rate change.