devices hostet in amxd~ take raw midi messages - no formatting should be needed when the input is coming from a midiin object.
so to play notes from a synth device, midiin to the rightmost input of the device should be all you need.
but i guess that when working in max, you will prefer to control parameters of devices rather by the first inlet, which take messages such as "parametername 0.5" - it works basically like in vst~ too.
in this case, midiparse.maxhelp is your friend. :)