re-initializing MIDI out?

while making an editor for the ensoniq esq-m synthesizer it seems like max having problems with the communication. it happens quite often that i have to restart max before the device answers a sysex-dump request. it sends it a few times without problems, but not often (5-10 before it needs another restart). especially after changing a program. i've put some delay between program change and dump request (500ms), and stopped noteout 500ms before program change - until 500ms after dump received.

that impoved it to the current state (before it needed a restart after any program change). since it always works after restarting max (reloading the patch has no effect) the esq has not to be switched off/on, only max.

so is there any function that re-initializes the midiout?