Odd question. Not really a software thing so here’s my hardware suggestion (bit of a hack).
Get a couple of Apple remotes off ebay and take them to bits. Find the pins for play, stop, pause etc… and connect each to digital pins on a controller like the Arduino or something which you can control from Max. Write your program and max patch.
uhm. how about sending them both into max msp at first.
then build a tapin tapout delay line for the first ipod you attach to a timer started by a tresh~ on input signal.
count the time between the start of the first ipod and the second by stopping the running timer upon thresh~ on audio start of second ipod. immediately set delay of ipod one to calculated delay, listen to delay only, and there you go.
also theory by now (no time to write example patch) but hey, might be working well without the need for further application terror :)