Good News!
Installed a Maestro SW for the steering wheel controls today. I now can get track skip and folder skip functions with playing a source in the background with Waze being viewed on the screen.
Setup:
2013 WRX (used 2012 WRX to program Maestro SW)
IPhone 5 running Waze
AVH-X8500BHS
Confirmed source mode behavior using up down keys on steering wheel (with Waze running in foreground):
Radio = press -> tune station, press and hold -> cycles through presets
USB2 = press -> skip track, press and hold -> cycles to next folder
CD = press -> skip trac