It works when I have one set up but as soon as both messages are simultaneously firing the process slows down a ton and gets tripped up.
It might depend on how the Arduino is handling (parsing/decoding) messages. Can you successfully send one message adressing one lamp, and after a pause send a 2nd message to the 2nd lamp?
What does it mean that the process slows down? Is there a latency (delay) between the time the message is sent and when the lamp reacts?
Is there a chance you are overflowing the serial input buffer while the Arduino's brain is off doing something else (like dimming a lamp or decoding the message)? I think
the buffer is 128 bytes, so I don't think you should overflow it with two DMX messages in a row...