You can use radio ra and aprilaire via rs232 with just an rp6, the drawback of doing this without an xp8 and zigbee is the 2 way feedback. With an xp8 and zigbee you can see the current temperature and your current temo setpoints, you can visually see your lighting zones current levels and which scene is active, with security you can get the screen feedback and current zone status, 2 way with receivers gives you a volume bar with current volume levels, etc... The displays i would do rs232 with just to eliminate the emitter eyesore. I would recommend the XP8 and Zigbee T2Cs, it's a night and day difference in the control capabilities.