The major advantage of the synthesizer is that it can generate any frequency you with to use within a certain band, so it is the equivalent to having all the crystals!
Multiplex has designed these receivers in such a way that is virtually impossible to set up the wrong channel.

They are programmed using a push button and ANY make of positive shift transmitter can be used.

The channel is selected using a button on the Rx, or a button on a parallel programming lead connected to the Rx. To determine the channel, the Tx is switched on with the aerial fully extended. and at a distance of 10m+. The Rx scans the band and detects it's own Tx. You can then operate the Tx controls to check the Rx is responding correctly. Only if this is successful, will the Rx be operated.