1) it is a reciever rather than ("only") being an amplifier
2) you can actually get one....it is (or seems to be) impossible to get either the A5 or E800 at the moment
3) coupla bucks extra
Apart from the "radio" I don`t think there are any differences between the two
See www.yamaha.co.jp for details and manuals
p.s. I think Richer have them at £260