For gigabyte z97x gaming 7, which IMHO has amazing integrated sound when powered with some nice PSU like seasonic etc, showed around 2,4V rms. Can't recall exact value now, I performed the test quite long time ago, but for sure it was higher than 2V rms, so pretty nice. But this mobo has been advertised as able to easily drive high imp HPs, up to 600 ohms.