here's the OS X version:
http://cl.ly/2c1Z321m2i22this only exists so I can debug the iOS app more easily, which has been in the App Store review queue for a week now and should be available soon (I hope.. iOS 7 is coming out next week so hopefully this doesn't interfere).
for the OS X version you need 10.7 or higher. (For the iPad version, once it becomes available, you'll need the Camera USB adapter and a powered USB hub.)
in the A4 MIDI settings, parameter output has to be NRPN, and output channel has to be TRK CHN. If you do this, the app will have optional patch sync, i.e. if you tweak a knob on one track, it will be mirrored over to the other tracks. this can be enabled/disabled at any time.
so basically start with an empty kit (or copy a sound to all 4 tracks using TRACK BUTTON + COPY/PASTE) and tweak knobs while playing your keyboard, for poly awesomeness.
You can of course use the patch sync on a kit that's not intended for poly play, giving you sort of a FUNCTION+knob-tweak functionality from the Machinedrum.. nice for messing up kits.
you can choose which tracks should be used for polyphony or unison, means you can have poly keyboard rotation e.g. on tracks 2-4 while track 1 is independently playing a drums/bassline sequence or whatever. The parameter mirroring is only enabled for tracks which are poly-enabled.
the app does not have split zones yet, and it ignores the channels of the note input device.
it also doesn't transmit aftertouch, only CC messages.
otherwise it should be straightforward to use.. if there's anything going wrong, let me know!