Actually (unrelated to Pi 3), audio was recently improved in an experimental driver.
From the engineer who worked on it:
> I reimplemented the original PWM-based 11-bit audio @48kHz as 7-bit 2nd-order Sigma-Delta modulated at 781.25kHz. The effective noise floor with this scheme approximates that of CD-quality audio DACs.
from the forums https://www.raspberrypi.org/forums/viewtopic.php?f=29&t=1364...