I assume you are using a USB-MIDI adaptor to communicate from Max to the H3000? That device will show up on your Mac as a USB MIDI device, which won’t work the same (programmatically) as a serial port.  You will need to either find a 4D plugin that will work with MIDI natively or find a bridge that will allow your MIDI device to appear to your Mac as a USB Serial device (at which point you can use the serial parameters specified here: https://midi.org/midi-1-0-core-specifications

Alternatively, if you can find a way to communicate into a Python script, we internally often use a Python package called Mido (https://mido.readthedocs.io/en/stable/) to do MIDI comms programmatically.

Hope that helps!