Third party control solutions
There is no RS232 control functionality with the Linn DS products.
The RS232 sockets on the Linn DS back panel are to allow the Linn DS to control other Linn products, not the other way around.
Linn products can be controlled by Philips RC5 command codes.
These are standard pre-amplifer (0x10), CD (0x14) & DVD (0x19) commands
They are listed here
The Linn DSM external inputs are selected by three discrete codes.
Details are listed here
UPnP ethernet control
By default the Linn DS/DSM is controlled by UPnP.
This can work as a standard UPnPAv device or as a Playlist device. Software such as Device Spy can assist with the commands and the format of these commands.
TELNET Ethernet control with LPEC protocol
This can be a simple way to control the Linn DS/DSM using AMX/Crestron etc.
All that is required is a TELNET port open to the Linn DS. This will allow you to control and get feedback as if you were controlling the LInn DS/DSM using UPnP.
Check LPEC for information