Hmmm... not so good for me. This feature would make an already excellent app the best app I've got if I could get it to work!
This is what I did, and what happens. First, I have an iTouch 2.1, running iOS 4.2.1.
1. I turned background audio off in iRealb.
2. I pulled up a tune, and pressed play. Song plays (sounds great btw).
3. I click the command button on my iTouch to access Amplitube...iRealb audio slowly fades out.
4. I open amplitube, and hear my bass playing...no iRealb song though.
5. Background audio is already on, so I leave it, though on a couple attempts, I turn it off then on.
6. I click the iTouch command button again to open iRealb, and my bass fades to nothing.
7. I activate iRealb, and the song I selected is shown, but not the play screen, and there is no audio. The song has stopped.
8. I open the play screen, start the song, it plays from 00.00, and there is no bass from me with it.

btw, I am using the Peavey Ampkit Link, but Amplitube has no problem with it.

Can you see where anything I've done is wrong, or if the equipment I have is just not up to it? I want to make this work in such a bad way!!!