I think you may have nailed the issue. Unfortunately I can't think of a solution to the buffer over running messages. If you don't need to send sysex from cubase you can shut off the sk880's ability to receive sysex in the midi config section. I think it's the same as the wk8 in that regard. If you are programing the board via sysex then... Do you send sysex at the beginning of a song or are these messages spred out over the song ? Sysex as you know can get pretty dense as it's being sent over a serial connection. I can remember choking a sequence I was sending from cakewalk to my outboard synth modules using sysex but I never had one lock up on me. The sequence would stutter like crazy until the sysex was finnished transmitting but then it would play ok. Maybe I was just lucky. It may be you are sending so much sysex that the processor in the sk880 can't handle it. One other thought are you playing the song from the sk880 into cubase or the other way around ? If it's from cubase to the sk880 (which is why you would have the sk880's clock set to external) is local on or off on the sk880 ? If it's on then that could cause the sk880 to lock up as it's getting stuck in a midi loop back.