I just went through this exercise, I upgraded to a Denon AVR from Onkyo TX-8050 for bass management in a 2 zone, 2 channel only system (see the mixed audio gear in my sig). The 1713 doesn't quite cut it, no Spotify. Pasted from a post in the xx13 thread:
Sorry Batpig, lets see if I have this straight.
The 1713 has zone 2 preouts, but no Spotify.
The 1913 has Spotify, but no zone 2 preouts.
The 2113CI is the only one that has both.
Extending this for what I subsequently learned, the 2113 has fixed (line level) volume out zone 2 when used as a preamp. The 2313CI has it all, so it's the one I own. Great choice, and my system with sub sounds worlds better now that my sub is properly integrated.