Most (all?) CD-ROMs output S/PDIF, not I2S. maczrool could make an *external* board which feeds in through the tuner interface, as this is designed to take an external I2S input (WS, bitclk, data) multiplexed onto the existing analogue lines.

This was intended to be used with a digital radio tuner. I've never tested it though, so there may be component changes required inside the player (possibly too much capacitance on the lines for good clocking). We'd also then have to do tweaks to the player for a digital-AUX mode, which would be non-trivial - though you could (in kernel) change the AUX in mode to send the correct DSP commands to select the secondary I2S input port.

Hugo