Most equipment that can be controlled by RS232, typically have a data sheet with pin out, baud rate etc along with the commands.

from there RTI programmers will use one of the processors, which will spit out the RS232 codes based on a trigger code from a remote. So you don't have to worry about which remote someone may use.

If you want to get fancy, you can create a "driver" for your Media device and do all this work for the RTI dealers. This will help get them on board using your equipment a lot faster. I assume you would have to contact RTI directly to find out more about how to do this, although there are a number of people possibly here and on the RTI forum site that can create drivers for you.
Ip control would require you to make a driver as well.

Good luck with your quest...