It's not exactly what you asked for but I have a Tivoli Pal and it's a nice device. It has a minijack input so you can use it with any portable player. It also has a good radio tuner so you could use it wirelessly with an iPod+iTrip. It doesn't satisfy your one device requirement but it also doesn't have to be plugged into the wall which is a nice tradeoff. I don't think it'll survive getting dropped in the tub but they claim "weather resistance" so it should be ok if it gets splashed.