Can't extend network: AE models the problem?

Question

checking out some other messages I searched out here, I suspect I may have the problem figured out, more or less, but need to figure out how to be sure:
I have 5 airport expresses, bought at different times, that make up a home network designed to play music via a pair of speakers attached to each AE, and one main is attached to a cable modem.
This works ok, though I get a lot of dropout as complained about by many others here, not consistent enough to blame my other electronics in the house, although who knows what the downstairs neighbor might have that is interfering.
Hoping to improve the robustness of the system, I tried to set up the AE to extend the network rather than just join it, but got a lot of error messages when airport utility was trying to 'configure main network' to accept an extension via this airport. I did type in MAC addresses for each additional devices into the main (modem connected) AE settings, under 'allow clients', and it seemed to reset with that data accepted/intact. I just couldn't 'extend' via the clients as I added them.
Which AE models are configurable to extend a WDS network? And does it matter which of them is the 'main' and which are the 'relay' devices? And can I interrogate the AE to tell which model they are or do I have to squeeze into their nooks and try to read the very fine print on them?
I really only need one of them to do the 'relay' thing to the printers, and if one of them is compatible with that function and the others were not, it would save a lot of time to know which one it is, or that I have to replace just that one.

Answer 1

Which AE models are configurable to extend a WDS network?
Both the 802.11g (Model# A1084 / Part# M9470LL/A) & 802.11n (Model# A1264 / Part# MB3211LL/A ) AirPort Express Base Stations can be configured for a Wireless Distribution System (WDS) to extend their network wirelessly. However, depending on which model you have, the configuration steps to do so are different.
There are basically two "flavors" of WDS: static & dynamic. The 802.11g models can only support static, and the 802.11n models can do either. In the case where you would use mixed versions, only the static option is available.
A static WDS allows for a main, relay, and remote base stations in the configuration. It is better suited when you want to cover a long linear distance ... like a rectangular-shaped building. On the other hand, a dynamic WDS only allows for a main and (multiple) remote base stations. This is better suited for those situations where the main would be in the center and you wanted to extend the network outwards to other rooms. Think of a star pattern.
And does it matter which of them is the 'main' and which are the 'relay' devices?
The "main" should be the one connected to the Internet.
And can I interrogate the AE to tell which model they are or do I have to squeeze into their nooks and try to read the very fine print on them?
The simplest way would be to use the AirPort Utility and check which firmware version a particular base station is using. The 802.11g models use v6.x; the 802.11n models use v7.x.