new airport extreme network very slow

I just bought the latest AE base station dual band, but am having trouble with the speeds. We have on the network:

1 macbook pro, 1 windows pc, 2 ipads, 1 ipad mini, 1 kindle fire, 2 iphones, 2 ipods (wow we have a lot of products I just realized now that I am writing them all down) a Wii console and 1 mac desktop computer. Oh and I have an airport express in another room set up to extend the netowrk.

Not all of them are on the network simultaneously.

Using the Airport utility (windows version) I have set up the network trying different configurations. Currently I have it set up as:

Radio mode: automatic

Radio channel selection: automatic

wireless security: WPA2 Personal

network options are 5 Ghz is unchecked

country is US

multicast rate: low

transmit power: 100%

WPA Group Key Timeout: 2 hours

use wide channels is checked

All devices can connect to the net, but speeds are at old dial up levels and that of course was NOT my intention in getting the latest router.

Any advice from those who understand things like multicast rate?