Hi Andrew,
Modified the protocol? I know that Sony flips between odd and even parity settings in the middle of the command. However, there is an easy way around that: just also send the parity bit itself. Don't check the partity, just send the bit. The camere will then receive what it expects. As far as I know for the rest it's just standard 38400 baud RS-422 or RS-232.
Joris