I currently have a T2-C with 1 RP-6. My system has expanded to three rooms of the house and I plan on adding 2 more T2-C's. My question is should I just add 2 additional RP-6's or bite the bullet on the XP-8?

Devices:
4 Receivers (RS-232 Capable)
3 Displays (RS-232 Capable)
3 Cableboxes (IR)
2 HTPCs (IR)
Xbox 360 (IR)

I would also like to do lighting and HVAC but I don't really feel like going the Zigbee route. Can I use RadioRa for lighting and HVAC and use RS-232 to interface with it via RTI processor? Thanks.

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.

XP8 for current capabilities and for what's to come. It might be two years down the road but you'll be able to remotely access your system, use a computer as a controller, or possibly control with an iPod. Time based events, relays, and way more sensing inputs (if I could get them to work) also make it worth wild.

Do I need to get T2Cz's (2.4Ghz Zigbee) and am I s.o.l. with two-way communication with my current T2C?

Yes, you need a 2.6 Ghz remote, and compatible processor (XP8 or ZRP6 in the near future). Yes you are SOL with 2 way on 433Mhz product.

What thefish said, but if you upgrade to an XP-8, you can use both Zigbee and 433 remotes with it, so you could just use your current T2C in a room that you don't need the 2-way feedback.

Anyone have any advice for the HVAC side, can't wire the controls so they need to be Zigbee and would like to implement homelogic interface as well. Advice?

Can you get Cat53 from the Mechanical room to the xp-8? If so just use the flush mount temp sensors spliced to the tstat wire. Put the tstat and dist panel in the mech room.

I havent controlled HL and RTi with aprilaire yet 2 way so you might need to play with that.

To do HVAC with RTI you're going to need Aprilaire or another 232 controllable thermostat anyway.  There's [currently] no 'native' Zigbee communication directly to a thermostat.  HAI has, or is coming out with, a wireless communicating thermostat, but you'd still have to interface with an HAI controller panel to the RTI system.

I see HAI has the RC-2000/1000 new HVAC controls, optional modules include the Zigbee Module and Zigbee Transceiver.

This is my first venture into 2way HVAC. Can someone walk me through the setup of the 2way HVAC using a XP-8 and RTI T2Cz.

Im guessing I need to connect the Zigbee transceiver to the RTI system some how (RS232) and connect the Zigbee Module to the thermostat and I "should" now have a 2-way link?