I´m Using Mac OSX Lion and PT10.2 and the SEM is useless in my system.
Not sure what to tweek to make it work better.
One instance CAN work, but i get stuck notes and High CPU usage errors, but I do not really see that much CPU usage in the System Usage window.
Use two instances and the plug-in goes havoc.
I tested 4 instances in Live and that worked great so I believe there is some mud in the RTAS plugin or the one being used (not sure).
So sad as the SEM sounds really great!