serial ports are hardware ports. If you want to send messages to 2 serial inputs on your arduino from the same computer, then you need a USB->serial interface plugged on your computer (does PCs still have a serial port?) and connect your arduino twice: one time over USB (this is Serial1), one time to the interface. Then you need to serial objects in Max
But this seems a very strange idea: why isn't 1 port enough to communicate between 2 devices. Or do I misunderstand something?
well as i was trying to send text to a lcd separating line 1, line 2 and controlling leds in same time, i though sending data for line 1 on serial1, line 2 to serial2 and leds on serial3 might maybe make it easier :)