I can explain how my system works, I have been through a few differnt types, and this is where I ended up, for the sake of simplicity and cost efficiency...
I run an AVR {audio video receiver} for my home theater system that has "zone 2" capabilities.
DENON AVR-2311CI 7.2 3D Home Theater Receiver | Accessories4less
Then run a set of rca's
Amazon.com: PREMIUM 6-Feet Audio Stereo Cable 22AWG Gold Plated 2 RCA M/M Plug Cable 2 M: Electronics from that units Zone 2 output to the inputs on a 2 channel 4 ohm stable amplifier
Dayton Audio APA150 150W Power Amplifier 300-812
then run the 2 speaker level outputs with 4 wire in wall speaker cable
Amazon.com: Cable Matters 4-Conductor In-Wall Rated (CM) 14 AWG Speaker Cable, 100% Bare Copper 100 Feet: Computers & Accessories from that amplifier to a distribution system, speaker selector
Amazon.com: Monoprice 108230 8-Channel Speaker Selector for Cellphones - Retail Packaging: Cell Phones & Accessories
then run 16-4 in wall speaker cable
Amazon.com: Monoprice 100ft 16AWG CL2 Rated 4-Conductor Loud Speaker Cable (For In-Wall Installation): Electronics from speaker selector to a volume control you install in each room
Amazon.com: Pyle Home PVCKT5 Wall Mount Rotary Volume Control Knob (3 Colors Included): Electronics
then run that volume controls outputs to each speaker in the room {2 in each room for 1 volume control}
Amazon.com: Yamaha NS-IW280CWH 6.5" 3-Way In-Ceiling Speaker System (White): Electronics you can use 2 sets of 16-2 for this or some of the left over 16-4 depending on how you want to do it...
That is about the basic setup, I have a similar yamaha speaker and I found them are the best value to sound quality for in ceiling units, they also sell dual stereo type speakers that will take both outputs and put out stereo sound from one speaker, so you only need one speaker in each room but still need 2 sets of cables and 2 outputs... I prefer the having 2 speakers...
Of course you can get which ever amp you want, which ever cable lengths you need, ect, I use 2 emotiva umc200 amplifiers, and 2 6 zone mono price speaker selectors, 6 zones in the house and 6 zones outside, zones 2 and 3 from a preamp processor, it works well, and the sq is very good considering, also it can play pretty loud... plus I can chose any content combo I want, we can be watching tv on the ht, and have the tvs sound playing throughout the house, or we can have the cd player playing through thte house and watch a blu ray in the parlor.... its very nice for ambiance, or when you are walking around the house and listening to the tv...
good luck I hope this helps, there are many ways to do it, and i used to have a high dollar multi channel amp and separate devices for each zone, ect, and it just to much, especially if you go a couple months without using it you forget how to control it and its like learning it all over every time, keep it simple, spend less money and you will be happy with the outcome...
PS- my brother only has 4 zones and just has one of them apa150 amps in each room, that all feed off the zones 2 on his avr but also has a little wall jack that accepts a 3.5mm plug from an ipod or phone, but his are much louder and he spent a lot on his in ceiling speakers, they sound really good and he built the apa150s into the wall so the volume control shows through and can be accessed in each room... so everyone does it the way that makes sense for them..
The htd systems are the next cheapest way to go and they are nice, I hear good things about them... With the system I have all 12 zones cost me under $1500 with the speakers, the amps, selectors, wires, and volume controls, not including the avr since I was buying that anyway... For 8 zones with one amp you can be in the neighborhood of ...
$160 for vol controls
$160 for the amp
$35 for the selector
$355 total then you need the cables and the speakers which will vary depending on what you want and need...