Some speakers aren't showing up in iTunes since upgrading to Lion.

I have an iMac running Lion and iTunes 10.4, my network is created by an Airport extreme. On my network there are three Airport Expresses, an AppleTV 1, and an AppleTV 2. All devices have the latest firmware updates.

In iTunes when I click on the AirPlay icon bottom right hand corner, I can see all these devices listed and can select each one individually and stream music to them fine.

My problem is when selecting the multiple speakers option, the only devices listed are the computer and the AppleTV 1, none of the other devices show. Strangely when using the remote app on my iPhone the multiple speakers all show and I can select them as normal.

This problem has started after the Lion/iTunes udate, but I don't think it happened straight away, I did a test install of Lion on a USB drive first and it worked ok on that.