A system comprising a processing module (101, 201) and a host device (121, 221), the processing module (101, 201) and the host device (121, 221) being adapted to be connected to each other via a communication interface (141, 142, 143; 241, 242, 243); the communication interface (141, 142, 143; 241, 242, 243) comprising: a command interface (141, 241) configured to transfer at least one command message between the processing module (101, 201) and the host device (121, 221) at a first data-rate, the command message having a command message format; and a transport stream interface (142, 143; 242, 243) configured to transfer at least one transport stream message between the processing module (101, 201) and the host device (121, 221) at a second data-rate higher than the first data-rate, the transport stream message having a transport stream format different from the command message format; the processing module being configured: to convert at least one command message to the transport stream format; and to send the command message from the processing module to the host device via the transport stream interface; and the host device being configured: to convert at least one further command message to the transport stream format; and to send the further command message from the host device to the processing module via the transport stream interface; the system characterised in that: the host device is further configured: to include the thus-converted command message along with the transport stream message to form a first enhanced transport stream; and the processing module is further configured: to filter the first enhanced transport stream to separate the further command message from the transport stream message. a command interface (141, 241) configured to transfer at least one command message between the processing module (101, 201) and the host device (121, 221) at a first data-rate, the command message having a command message format; and a transport stream interface (142, 143; 242, 243) configured to transfer at least one transport stream message between the processing module (101, 201) and the host device (121, 221) at a second data-rate higher than the first data-rate, the transport stream message having a transport stream format different from the command message format; to convert at least one command message to the transport stream format; and to send the command message from the processing module to the host device via the transport stream interface; and to convert at least one further command message to the transport stream format; and to send the further command message from the host device to the processing module via the transport stream interface; the host device is further configured: to include the thus-converted command message along with the transport stream message to form a first enhanced transport stream; and to include the thus-converted command message along with the transport stream message to form a first enhanced transport stream; and the processing module is further configured: to filter the first enhanced transport stream to separate the further command message from the transport stream message. to filter the first enhanced transport stream to separate the further command message from the transport stream message.