OK, this is interesting ...
I have an iPad3 with 30 pin connector, and if I connect the iPad to the DL's 30 pin connector, now I get both the DL1608 and Airport Express as Airplay options
If I select Airport Express, I can play music through the router and it comes into the DL through channels 15 and 16 as normal.
If I disconnect the iPad from the DL's 30 pin connector, I still have an Airplay connection to the airport express and it will keep playing while MF3 is in use
If I close MF3 and re-open, then I lose the Airport Express as an Airport option, as Ampli reported
I cant get Airport Express to show up as an Airplay option unless the iPad is connected to the DL, but if I do that, Airplay survives the disconnect
This is not ideal, but I can live with it until Mackie fixes it.
Ampli - when you got Airport Express to work, were you by chance connected to the DL?
Rockit - if you connect to the DL, can you get Airplay to work?
edit - Rockit, I just re-read your post and it sounds like you were able to establish Airplay to express while docked - just still not working right for you for some reason. If you start playing iTunes over the Airport Express while the iPad is docked, can you then undock and keep the Airplay connection?