Which Airport Express....?

[Damon]

3. And does it replace one's wireless router or is the airport express plugged into the existing wireless router?  And then the dialogue connects with the express? 

I can only offer a bit on question 3. As I understand it, the AP extreme may have a better or stronger wifi capability than the AP express. It may also have more ports for physical connections and support more wireless protocols / types. I do not think it will replace your existing router. Typically an Airport adds another wireless network, or adds the first wireless network if your router does not have wireless capacity. The AP connects via ethernet to your main router. The AP Extreme is, I think, primarily intended to be used as a wireless backup device, so you will be buying an external hard drive inside the AP Extremet.

I know very little about modems and routers, but I believe that there needs to be some matching or compatibility between the modem/ router that connects to the wall, and the internet provider. Possibly, as I say. Others will likely correct me on this point.

Wireless networks can be strange. When I had my Naim gear, I could not reliably stream Radio Paradise or Jazz24 from KPLU in Seattle. Now with the Devialet, with the same internet connection and router I can easily stream any radio station without a problem. Things are strange in the world of wireless.