Wow, this might be valid for live...

[dflat]

...So once your track has an intro, and ending, you still need to input tempo and number of choruses? Is that right? Also I've just installed AmpKit+ and would love the two to work together.

Any chance?

Yes you need to set tempo or tap to get it (assuming the one it has is not what you want) and number of choruses. Can be done quite quickly though.

As far as I know AmpKit+ does not work with audio from another app as input. We have had another thread here:
http://irealb.com/forums/showthread.php?t=830
relating to this. We will look into this in the future and see if it is possible to sum the audio. Multitasking has just been introduced for iOS (and not yet iPad.) Obviously we also need to make sure the CPU can handle the demands of both.
Meanwhile you could record the audio of iReal book tunes at the correct tempo, key etc. and add it back via iTunes into your music/ipod library, then use guitar amp apps that can play them while adding your guitar effects. Not as spontaneous, but should work.

update Sept 2011
Ampkit v1.2 includes multitasking support so audio is processed the background
http://agilepartners.com/