In reply to Dave:
In the end I went with Sonos. I did look closely at Simple Audio, and it's possible it had the edge on sound, but the sonos app for controlling was better, sonos had a slightly lower price and also, as a company they seem to have the critical mass to last a while, while simple audio was younger. This was two years ago, I've a three part sonos system which will grow by 1 or two bits at Christmas, (fingers crossed).
nb - I don't use apple, so can't vouch for either system with that. Sonos did drop bbc radio sports broadcasts earlier in the year, but the patch comes next month. Basically bbc couldn't tell if you were listening to the game in a country they could broadcast too.