well it would require a loader program similar to the flash carts
the system side interface would be serial data stream on 1 or 2 ports depending on the system used
4 bit status and interface data compliant with the sony CXD1167
in the duo the CXD is switched between data and audio modes, but in the CDR2 it remains in data mode
the rest of the system would remain intact as it would still need to route data to the CORE/PCM/DAC
note the DAC is expecting 1 data line, 1 sync line, 1 bit clock and 1 L/R clock (4 pins)
everything else is controlled by reset, interrupt ,parallel bus or serial data, direction, frame