Extend Time Capsule network with Airport Express?

I'm having a *hell* of a time getting this set up.

I have a Time Capsule and an Airport Express. The TC is connected by wire to a cable modem/router. I have cables in my house that allow me to run a CAT6 out of the TC into the wall, down the hall, to where I would like to set up an Airport Express to extend my wireless network range and run a pair of speakers. Ideally this would all be seen as a single wireless network.

What network setting do I need on the TC and AEx to get this all working? Can you be reasonably specific. I feel like I've tried everything.

That looks promising.

Really...this should be easier. I'm a geek and this isn't that straightforward! Seems like an "obvious" thing to want to do. I'll post more if this works...

I posted this in the other thread...

This seems to have worked for me. I have a Time Capsule that is connected to a remote Airport Express over Cat6 that runs through the walls of my house. To get around the problem in (6) I made sure that both networks were set to the same channel. Everything is happy.