Are the four speakers broken into separate areas, or are they all controlled with the same volume at the same time?
If you want them all playing at the same time, at the same volume, then a surround receiver set to '7 channel stereo' will do the trick nicely without a lot of cost. You wouldn't even need a two zone receiver.
On the other hand, if you want each zone to be controlled individually, then you will need a two zone receiver or some other setup to accomplish this. I think the two zone receiver is the easiest way to give you independent volume control and generally offers built in zone 2 amplification.
You can then get any CD player you want. Most decent A/V receivers have built in FM tuning and XM/Sirius radio is now very common as well as iPod playback options.
They go beyond what you need as they handle video and a ton of other stuff, but because they are 'popular', their price is also far less than what you may end up spending on other options.
Still... Other option:
Amplifier:
Sonance Sonamp 260 MKII 2 Channel Amplifier | eBay
Two zone volume control:
Niles SVL-4 4-pair speaker selector with volume controls | eBay
Source selector:
Zektor HDTV Audio/Video Switch HDS4-SLV | eBay
You can see things are starting to pile up and add up, and with only two zones then a receiver may be a better choice.
Something like this sounds good...
DENON US)
But, if you want to run the speakers in the second zone at a different volume level, independently, or with a different source then you will need to purchase an additional amplifier to power zone 2.
Instead, something like this is more ideal:
DENON US)
While that's brand new, you can really go for a model a couple of years old which is in good shape for just a couple hundred bucks or so. You don't need the latest and greatest in video compatibility it seems, so for audio, the technology from a 2310 or similar should do you just fine.