hey dsound, i’m not sure i get this right but syncing via audio doesn’t ring any bell to me in this case…
you can sync the AR/AK via MIDI (choose who’s the master and who’s the slave… 
) make sure you set the master to send MIDI Clock/Transport to the slave and that the slave is actually set to receive those signals
I have the AR and AK. Can I route the audio out of the AR to the AK and hear them both through headphones from the AK? If so, how do I set that up in the AK?
yep, simply get the audio output from the AR (Left+Right channel) to the audio input on the A4. you may want to check this post as well for more ‘in-depth’ suggestions 