Roaming WiFi without AirPort Extreme at core?

Question

OK, I'll try to explain my situation in detail...here we go.
Moved into a new house that is wired for Ethernet and signed up for Comcast's new X1 Platform.  I have all the comcast equipment in a media closet in the basement and originally wired the modem via Ethernet to the main floor where my prior generation AirPort Extreme sits.  I didn't realize the new X1 box is not just a modem as I was used to...it was a modem and a built in WiFi router.  So I was getting blinking amber on my AirPort until I put it into Bridge mode and now it works fine.  I researched putting the Comcast box into Bridge mode but with X1 they've locked them down.  It requires a call to support...and it sounds like a lot of headaches (plus I wanted my AirPort on the main floor, not the basement).  So for now I've left it and basically ignore the WiFi signal coming from the basement and just use the AirPort extreme in Bridge Mode.  Works great!
Fast forward to today and I want to strengthen my signal to the upstairs.  I took advanage of a Black Friday deal and have a new current gen AirPort extreme here in the box.  I want to create a roaming WiFi network as outlined here:
http://support.apple.com/kb/ht4145
My question, however, is that the Knowledge base very clearly shows a main AirPort base station controlling the roaming network...this image:
http://km.support.apple.com/library/APPLE/APPLECARE_ALLGEOS/HT4145/HT4145-3.png
Is that a requirement, or if I have two Extremes both in Bridge mode with the same SSIDs, Security, etc will the roaming effect work?  Or will my devices try to hold onto the old access point for as long as possible and not jump to the new one?  Just to be clear, the setup would be:
X1 Modem/Router Combo --------AirPort Extreme (current gen) in Bridge Mode
                                       |--------Airport Extreme (prior gen) in Bridge Mode
Sorry for the convoluted question.  I tried this once before with an original AirPort Extreme (UFO) and the devices would not roam...they'd stay on the original access point and I'd need to manually switch.  I'd love to get roaming working!  Thanks all.

Answer 1

My question, however, is that the Knowledge base very clearly shows a main AirPort base station controlling the roaming network...this image:
http://km.support.apple.com/library/APPLE/APPLECARE_ALLGEOS/HT4145/HT4145-3.png
Well, Apple assumes that you will only be using Apple AirPort wireless routers in their support docs.
Is that a requirement, or if I have two Extremes both in Bridge mode with the same SSIDs, Security, etc will the roaming effect work?
Roaming will work fine if both AirPorts are set up the same as you indicate.
Or will my devices try to hold onto the old access point for as long as possible and not jump to the new one?
The real question here might be what devices you are asking about.  Mac computers are very good about scanning to find the best access point and automatically switching to pick it up.....but a lot of PCs are not very good about this.  iOS devices like the iPhone and iPad are not very good about this either.
If I walk my iPhone from one access point to another, it will hold onto the original access point...even if it is very close to an access point with a stronger signal..Nature of the beast with iOS, I am afraid.
Sometimes, the iPhone will switch, but usually I have to switch off the Wi-Fi when I move the iPhone close to another access point, and then turn it back on so that it will then pick up the signal from the closer access point.