I primarily use AUM and enjoy routing several apps on different channels, route them through effects, bus them, and use various midi apps and sequencers to produce the sounds. Having the ability to assign MIDI commands to the controls would be a nice addition to KRFT. An ability to do MIDI program changes to switch between surfaces would be useful too. Getting a sequence going and having the ability to accompany it with live play is enjoyable for me.
A critical ability is to be able to sync to the IAA host bpm as well as being able to respond to the host transport controls. One way this would be useful would be to have the ability to assign a start command to one of the Loops or Groups in your surfaces which would be to start playing in sync with the host start button.
Link is very nice for jamming which I do quite a lot. It allows for multiple device setups and to have time based synths and effects to be in sync with each other.
Audiobus has nice state saving features and Audiobus remote which allows for some straight forward recall and playing of IAA setups. Audiobus 3 will offer further improvements.
Moebius lab is another IAA host that allows for some very interesting feedback loops and effects. ZMors Modular has lots of options and supports a wide variety of protocols so it is great for experimentation.
When I want to record a song, I'll use Cubasis with IAA synths and effects.
At times GarageBand has some nice IAA options too.
I also use IAA for recording loops for use in other apps or compositions.
I also have various MIDI hardware controllers I use to play IAA synths and effects.