Sadly that setting seems to be a hit and miss, sometimes it stops iTunes from playing while importing but other times not so much. If anything it seems it depends on how you import it. Ripping from CD seems to honor this setting, but importing by DND onto the iTunes windows not so much. But to be honest, even in iTunes 7-8 when that setting was visible it still was buggy.
So to OP, flip that switch and see if it helps, there is sadly not much else you can do at the moment.