This is one aspect of the RNSE that is greatly understated. In addition to all the nav / BT / sat / MP3 bells and whistles, you get a "higher" end headunit.
In the world of aftermarket car stereos, the quality of sound can be measured by THD (total harmonic distortion). The lower the number the better. I imagine the RNSE follows this same principle...but haven't seen a spec sheet to confirm.
Also, as a point of reference -- I have a 2001 A6 avant without bose and have been told many times that my RNSE sounds way better than any Sym II WITH Bose. And I'm still running the same crappy stock speakers that came with my car 5 years ago. Go figure. At some point, I'll swap out the door speakers with something better....but keep the same factory amp configuration.
Hope this helps.