Actually, probably not. The RS4 or RS5 board won't recognize the the Legacy serial data, so if you attempt to run the R4LC-Sx in Legacy mode, you'll have audio issues, most sounds won't work. You have to have a Legacy RS 5.5 board to run it in Legacy mode. I have a RS4 board and an R4LC-S03 in my test rig, audio is MIA. The bell works, no horn. Startup doesn't work, but if you hit reverse you can get sounds. I have a diesel board in there now, no ramp up when I increase the speed, it remains at idle.
If you want to run in Legacy mode, you need a Legacy sound board.