There are a couple of options that I have looked at for doing this as well. Either you can go with wired or wireless solutions.
I managed to run speaker wire behind the walls when renovating for 5.1 in the family room and for speakers in the kitchen and sunroom all running back to a central point that will be able to provide sound from a 3 zone reciever. Still painting and have a kitchen to put in before I get to connecting up speakers yet, but at least the wire is there if I need it.
The AV recievers normally can only do a few zones and definately not up to 8 that I have seen anyway.
The other option is to go for a wireless solution. The Sonos looks like a great solution http://www.sonos.com but it depends on your budget. The The Sonos ZonePlayer 90 is where you would have your network connection for internet radio as well as plug your Reciever with LP, IPod etc.
logitech have a similar product which is a bit cheaper.
Would love to put something like the Sonos in but at this stage I have a kitchen to pay for :)
I think it's important to think about several things when you're looking at designing something like this. Most important is how you intend to use the system. If you want one source playing back throughout the house, that's may necessitate a different design than having several independent "zones" in the house.
Where will your music sources be located? Your turntable will feed one amp, which would power two or three sets of speakers at most. If you've got a music server in the basement, you could stream music to multiple different destinations at the same time.
I like the look of the Logitech Squeezebox Duet. It's got a handset for browsing and controlling playback, and a base unit that plugs into the amp and your network. You'd have a Duet in each room, connected to a single-zone stereo amp and speakers.
My understanding is that with the Duet, multiple handsets can control multiple base units. This means you could have each base unit playing different music, or have one song playing synchronously through all the base units. You'd want to check I've got that right before investing in half a dozen Duets though!
The lovely thing about this is that it's scalable and distributed; each room needs a network connection, a Duet, an amp, and some speakers.
The alternative is to have a central amplifier controlling speakers throughout the house. You'll have a hard time finding an amp that can handle eight pairs of speakers, and you'll likely be much more limited in what you can play back to where.
In short, I reckon digital distribution is best, with separate amplifiers wherever you want your speakers.