The file omxSadmvnWrapper.cpp has the following hard-coded precision options for numerical integration:
double absEps = 1e-3; double relEps = 0; int MaxPts = 10000*cov->rows
1000*ordCov->rows * ordCov->rows * ordCov->rows;
At the same time, providing mxOption() access to absEps and relEps would help to eliminate possible numerical precision related issues. Could that be added?