I have finially worked out how to write a program to change the volume on RSMeida (without the remote!!).
The program is called 'rsmvolume' and you can download the program and source from here (PS let me know if you have troubles getting the files - I haven't released files from this type of sorceforge link before).
Read the README.txt file for information on how to run it.
The program can be used from the console command line (like USB console or serial) or it could be used in a script or bodycon. But I suspect that it will be most useful for the other 'addon software' for RSMedia like the 'RSMedia Contorl Station' where it could be used to adjust the volume of RSMedia from the PC.
Hope you find it useful !!