Either approach is possible. If you centralise all of your amplification you can then feed your amps with audio from device like Squeezeboxes or Squeezeslaves (soft versions of a Squeezebox...see the wiki). If you decentralise all of your Amplification into each room or zone and have local MD's or Squeezeboxes in those zones then you gain some flexibility (each room has its own sound source for example) but you have to find space for the equipment in each room or zone (and potentially the noise of the devices themselves if they are not passivley cooled).
Flexibility is nice, but not at the expense of having to find an amp for every pair of ceiling speakers and then somewhere to install the things! So, I'm going to stick with my "running all speaker wire to the basement" idea. I lose some flexibility, but if I can get an amp with enough zones, at least I'd get some of that flexibility back.
Would I be able to control the MD connected to the amp/receiver from a different MD? For example, if I'm in the family room and I want to play music in the living room, could I use the family room MD to tell the MD in the basement to play music in only the living room zone? From what I understand, I could with multiple sound cards (e.g. USB sound cards) connected to the MD in the basement.
Either approach is doable...and its possible to intermix the the approaches in a single installation too (just to confuse you!!)...some zones having centralised hardware and some in-room hardware.
This is good to know. I can see this happening in my home.
All the best