As far as I know the issue with WIFI is that it is not possible to "change networks", even extended ones without a proper reconnect. 

For the ultimate we install a wireless mesh system in large properties. Can be expensive.

Recently on a large install (Playmakers all hard wired) we installed this router non WiFi version:

link

With this single Access point:

link

Fl_5F00_ip wrote:

We use a lot of the Unifi series also. Normally the Unifi Pro

I am not a wifi fan - anything that bathes people in microwaves is inherently dangerous.......

In your case the simplest option could be buy a Hilti masonry SDS drill and some long masonry auger bits ( say 12-24 inch ) and drill through walls and run some 1 GB Cat 6A cabling and buy a 1 GB 5 port local ethernet switch and run a wired  wired connection to either another wifi unit/repeater, or just plug into the cable directly.    

Simple = robust.

How large is your coverage area? If AirPort Extreme with extenders won't work, it may be simpler to invest in a business grade solution such as Cisco 541N router with built in wifi. There are also other options with business grade access points which should provide good coverage for about 2500-3000 square feet.

Apple are shortly bringing out a new more powerful router that's meant to be good - I use a couple of  airport express to extend my network wirelessly as the building is around 250 years old with thick walls. It works really well with no drop out when moving from one zone to another and streaming music from my iPhone.

Thanks for all the advice, will look at all the suggestions and work out which one suits my needs best.

I plan to wire the house with cat7 cables which will over the ML, PL, and ethernet, and then have wifi for my ipad and the beolit.

Thanks

Toby