I didn't mean to blame sndfiler, I was just asking for the right way to do load a soundfile.. ...I thought it had something to do with threads priority because I had a similar problem with a flext external I wrote: if I start pd with -rt and run the second thread and this thread is very cpu expansive it gives droputs and can even crash jack! i and I took care to set a low thread priority which seems to stay higher than normal anyway..
anyway, back to the original problem: I will try Derek's samplemapper and Miller's workaround...
ciao, davide.