Generator X (silver) is the dual channel device. The XM is only a Single generator. Yes, it has 2 outputs, and there are ways to put different, but related frequencies on different outputs - and some advanced users may use two remotes at the same time, but in most instances, the Boost is less expensive than another remote, and the signals are combined in the boost so both outputs go through one remote.
The user gets the benefit of all that the generator can do with only one remote.
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