An Express cannot amplify wireless ever..
It can act as extender to another Apple wireless router.. but no other brand.
I would strongly recommend you buy a repeater based on the exact hardware you already own.. or plan on connecting various wireless items by ethernet..
The problem is wireless repeater tends to be propriety. Apple routers cannot extend wireless for other brands.. and many other brands cannot extend wireless for apple. The old wireless repeater codes were not updated from WEP security.. and so each company does what they think is best.
You can buy universal wireless repeaters but they work poorly.. !!
And I strongly encourage you not to wireless repeat at all.. due to the fact that it will slow the network down drastically.