IFixit has now updated its site, saying that one of the chips is the InvenSense ITG-3600.

For those who are wondering, I have been looking at IFixit's tear down of the Apple TV all morning. Microphones are typically not identified, and in this case I can not identify any sensor chips for sure either.  The ST Micro ASC Y523 chip has about the right external characteristics, though.  Going forward, I wouldn't be surprised if all of the motion chips that Apple uses are dual-sourced.  That means that InvenSense management's guidance is the best forward indicator for the business.  Nonetheless, Chipworks should be posting iPhone tear downs soon, and I will report when they do.