RS232 is an electrical specification that defines a physical connection method and Homey doesn’t have an RS232 connection.
The link you have given is a list of commands that would be sent over an RS232 connection. There is nothing there to define how the commands would be sent of TCP/IP, e.g. which port to send the commands too, etc.
I also have a amp which can be controlled by rs232. I made a arduino sketch with a arduino board and a rs232 expansion board (about 10 euro total) and use the homeyduinio app over WiFi. But you have to build it yourself.