The information on the two models is kind of scattered across their main and US sites, the reservation form can be found on the US site.
https://www.audiusa.com/technology/efficiency/e-tron
http://www.audi.com/en/innovation/futuredrive/e-tron_quattro.html
https://www.audiusa.com/technology/efficiency/e-tron
http://www.audi.com/en/innovation/futuredrive/e-tron_quattro.html