6600M control by another 6600M?

The front panel of the M model radios do not operate like the Maestro. They are connected to the radio internally by a local network connection. I have never seen a way that you could bypass the radio's internal connection and connect to another M model radio from another M model radio. Even given the scenario you presented, I cannot imagine why you would want to do that. If you have an iPhone or a tablet ( iPad or Windows tablet) you can easily setup and use those compared to trying to connect the front panel of one radio to another.

James

WD5GWY

not to be rude, but I will be surprised if Elecraft ever does implement such a feature in the K4 line. Either way, it is an expensive way to operate one radio from another.