StartupSound.prefPane on new iMacs? Inspired by this question to which I thought I knew the answer, does anybody know how to make StartupSound.prefPane work on a new iMac?

I just got the computer last week, and installed SS.pP (v1.1b3) right away, but noticed the next day that it didn't actually function.  However, it appears to work, in that it installed fine in System Preferences, I can access it, check and uncheck its options, and move its slider, all without receiving warnings or errors of any kind.  Whatever configuration I set is remembered the next time I go into the app, even after a reboot.  Nevertheless, the startup sound is still played when I boot up.

Edit: Are others having the same issue?  I'd be interested to know if this is a consistent problem with new iMacs or some quirk in how I've set mine up...
Unfortunately, I'm pretty sure you're out of luck. A year or two ago Apple decided that the startup sound is enough of a diagnostic (which it is, in fact: it lets you know the logic board is functioning properly enough) that it needs to sound on every boot, from the internal audio device, regardless of what your sound settings and interfaces are.