If you have an external clock that's transmitted exclusively over an analogue channel, then everyone would hear the beats at the same time (barring speed-of-light transmission times, which is really only a factor if the transmission uses geosynchronous satellites). But if there is any digital transmission then you're back to the same problem. Not everyone will be the same number of router hops from the source, so with a digitally transmitted clock players may hear the beats at different times. If not, then it's fine for each player playing by themselves -- but they won't be able to hear each other (which may make playing as an ensemble difficult; I don't know, I'm no musician). And also, you're left with the problem of transmitting the music from each player -- if it gets transmitted over a digital channel then you have the "different lag from different router hops" problem all over again, and you'll hear the different lags from each player. The human ear is a marvellous instrument, and very intolerant of sounds being out-of-sync.