Well, back on topic...... I've managed to get an old version off an iPad using iTunes 12 on a different computer (i.e. not the one it was synced to). There were no apps in this iTunes instance, it's my studio MacPro and I just use iTunes for music playback in the studio. I plugged the iPad with the old app version into the computer, told it to 'trust' the computer and used 'file>devices>transfer purchases' to the MacPro. I just ignored the 'wipe and sync' messages etc.
I'm waiting for the guy over on the X32 forums to try it and get back to me.