sure, for example:
connect the a4 headphone out to the ar sampling input: this way you can sample sounds from a4, and if you connect other signals to a4 audio in, you can also sample those signals, even with a4 effects or thru an a4 voice circuit… all for quick sampling in the rytm
a4 has four cv outputs plus a cv sequencer… ar and a4 have two cv ins each, which can control various parameters…
you can control the performance macros of ar from a4 and vice versa:
also you could send two individual voices from ar to a4 in, process them and feed them back in the ar…
the possibilities are very deep, nearly endless, i think…