While the range of the router provided by your ISP may or may not be greater than that of your AirPort Express, you could potentially use your AirPort Express to extend the range of your WiFi network, thus putting BOTH to work and combining their power!
This can get confusing, since we are talking about two different things here.
It is possible to turn off the wireless function on the FIOS router, connect the AirPort Express to the FIOS router using a permanent Ethernet cable connection, and use the Express to provide your wireless network.
That's a lot of work, with no assurance that there would be any improvement if you did this. Unless you are confident in your abilities and adept at troubleshooting, it would probably be best to leave well enough alone and use the FIOS router for your wireless service.
It appears that Allen was suggesting that you use the current FIOS router to provide a wireless signal and the Express (located a few rooms sway) to "extend" the FIOS router signal wirelessly.
That won't work, since the Express is not compatible with the FIOS router for this purpose.
Thank you so much for explaining. I think you're making a good point. Sometimes it's best to leave things alone. I just hated to give up my Express that I recently purchased. Did you see the Apple conference today? Now I hate waiting so long to get all the new things. Have a wonderful week Bob, and thank you again for your help.