Review of Phoenix Gold
Check out the review of the Pheonix Gold ATc6 in-ceiling speakers and VMT-100 volume controls I used and my system:
http://forums.audioholics.com/forums/showthread.php?t=34083
The construction of the Phoenix Gold speakers and especially the VC is very similar to the products from HTD. For about $60/room shipped you can get the speakers and VC I used, the speaker selectors are optional when you have the impedance matching VCs. Try it first with your current receiver and if it doesn't have enough power (speakers are not loud enough in each room) then add a more powerful stereo amp like the Behringer A500.
Here is a simple calculation. If your current receiver has 100 Watts per channel / 9 rooms, you will get a max of 11 Watts per speaker. One of the A500's can deliver >200 Watts into 4 ohms or >22 Watts per speaker.
I would still plan on getting an HT receiver w/ Zone 2 ($400+) and an RF remote ($100+) to help integrate the control of your main and distributed audio system from upstairs.
Distributed Audio System
Speakers and VCs: $60 x 9 = $540
Speaker Selector: Optional
Speaker wire: $.25/foot for 16/4 and $.15/foot for 16/2 from Westlake Electronic
Behringer A500: $180
Main HT
HT Receiver w/ Zone 2: $400+, Yamaha RX-V661 or similar
Universal Remote w/ RF: $100+, Check out products from URC