First post!
I had an airport express issue which sounds not dissimilar. My experience is also probably slightly more out-of-the-ordinary than most, as I travel so much.
I bought an AExp while I was staying in the USA so I could have wireless around the apartment, and after the initial setup (which was pretty painless) it worked fine. I don't remember ever using the admin utility after that and I didn't have it plugged into a stereo so didn't use airtunes either, although I remember iTunes detecting remote speakers.
When I got back to the UK I started having problems. There's already a wireless network in my house and other networks in the surrounding houses that show up from time to time. I set it up for our network ok and connected it to my stereo and initially, it worked for internet and airtunes, but after that there were problems. The first thing was that it wouldn't connect to the remote speakers, then I couldn't detect it in the admin utility. I tried a hard reset eventually but it didn't stop flashing amber and I still couldn't detect it. I found that if I shut down my MBP, reset the AExp then turned my MBP back on, I could detect it in admin utility and go through set-up type stuff, only to have the same problems all over again. I sent it to apple, they reported no problems and sent it back.
My last resort was to downgrade the firmware - I went from 6.3 to 6.1.1 - and it worked like a dream! Why it worked with 6.3 in USA and not UK, I don't know, although I suspect it had to do with the different ways I was using it, not where!
I hope this fix helps others, I saw a load of threads about AExp problems that each helped lead me to the firmware downgrade solution and so I thought I'd share this.